So, there seems to be something of a disconnect here.
I'm describing an explicit claim, made by the World Tree cosmology. This isn't me inventing a thing. It's something canonical to the World Tree.
Yeah, I sensed you were referring to a difficulty that the Tree cosmology officially causes. I will parse it line by line as I go thru it. (Thanks for finding the quote below.)
The overall impression is, the Wheel and Axis search engines can easily list links to many websites in the multiverse, that the Tree search engine actively censors.
Here is a schematic map of the Tree cosmology, I assume it is official or at least representative enough.
If I understand this map, then each plane is a separate website in the Astral internet. The Tree search engine groups the links to these web addresses into four groupings: Celestial, Fiendish, Neutral (?), and Elemental (the Inner Planes?). Toril is the planet of the Forgotten Realms setting. The planet itself is functioning as the search engine page, that has all the links that one can click to get to any of these particular websites in the internet.
Notably (if I understand correctly), there is no Astral Plane! Or rather, one cannot use the Tree search engine to click to the Astral Plane. (The Astral Plane is part of the "dark webs" that the search engine doesnt link to.)
For example, one of the Celestial Planes is Arvandor. There is a direct line connecting somewhere on planet Toril to Arvandor. This line is like a wormhole tunneling thru the Astral Plane, to get from Toril directly to Arvandor. When "shifting" from the frequency of Toril in the Material Plane to instead attune the frequency of the Arvandor, there are virtually no frequencies in between, no "distance". This is a "portal". Step thru the portal, and one is at the new frequency.
The Tree cosmology is actually a map of portals. All of the portals are somewhere on the planet of Toril.
(Note, there are portals linking back-and-forth between Arvandor and a plane called Cynosure, but only Forgotten Realms deities can click on these links to access that other website. The Arvandor-Cynosure portal way has no connection to the planet Toril.)
With the map of the Tree cosmology in mind, I am now going thru the passage you quote.
Having read more closely, it seems that the strong claim is different, but not dramatically so.
In the D&D cosmology, the Astral Plane surrounds all the other
planes in a shapeless cloud, allowing astral travel directly from one
plane to any other.
Essentially, the Astral Plane does exist, but it is difficult for the Tree search engine to find it.
Here in the Tree, the Astral Plane "surrounds" the other planes.
I would say more precisely, the Astral Plane "overlays" all planes that exist anywhere. In the sense that Astral "contains" every plane, where the Astral exists but a particular plane doesnt, the Astral can be said to surround that plane (as well as overlaying it).
But Toril’s Astral Plane shares the treelike shape of the cosmology as a whole.
Because Toril uses the Tree search engine, one can only click on the links that are on planet Toril. Each link wormholes thru the Astral Plane, directly to the website address of the other plane. For example, clicking on the Arvandor link gets to there immediately. There is no stopping point somewhere "in between", such as somewhere in the Astral Sea.
Because of this arrangement, it is difficult (though not completely impossible) to jump from branch to branch of the tree—that is, to cross directly from one Inner Plane or Outer Plane to another.
This statement makes sense. The Tree is the (cultural) cosmology that the inhabitants of this planet use as their methodology to navigate to the websites that are in the mindscape of the Astral Plane.
Because of "this arrangement" − the way that the Tree search engine discovers, evaluates, and prioritizes the websites − it is "difficult" to jump from branch to branch, namely from one website directly to a different website, without first returning to Toril to click the link to that other website.
Difficult but not impossible, because Arvandor itself has portals to click on to get to other websites. (Arvandor itself in my view borders the Astral Sea, so one can go thru a kind of planar "crossing" to find oneself near the edge of a floating island in the Astral Sea. From there one can sail the Astral Sea.) However, the Tree search engine cannot find these other links that exist at those other websites.
In sum, the Astral Plane exists, but the Tree doesnt list a link to click to there.
(See Traveling the Planes, below, for more information.) It is more natural—and far safer—to travel between the Inner Planes or Outer Planes by way of the trunk (the Material Plane).
Heh, this is a kind of cosmic censorship. It is "safer" to only use the "official" links that the Tree search engine supplies. Yes, there is less risk of "malware", but also less opportunity to disagree with the Forgotten Realms "gods", the dictators of Toril.
As part of its ability to alter the nature of its realm, a deity can forge a direct connection to any other deity’s realm, so long as both deities agree. Apart from divine influence, however, such direct connections are impossible.
Among the Celestial, Fiendish, and Neutral (?) websites, the rulers of these websites agree by a treaty to remove any unsanctioned links between each other.
Travel from one Outer Plane to another is slightly more complicated. Normal astral travel cannot take a character directly from one plane to another except by way of the Material Plane.
"Normal." Travel across the Tree only allows access via official routes. There are whole universes in the mindscape of the Astral Plane − that the Forgotten Realms "rulers" dont want Toril to see.
A character or monster can use plane shift to move directly from the Material Plane to any other plane or vice versa, but not from one Inner Plane or Outer Plane to a different Inner Plane or Outer Plane.
Interesting. The Forgotten Realms deities are directly interfering with spellcasting. This apparently relates to their control, regulation, and censorship of the "Weave".
3e Player's Guide to Faerun, p 139-140 (two separate but related sections)
The structure of Toril's Astral Plane is tree-like. It specifically only has "branches" connecting one plane to another. You have to do a very dangerous thing in order to even attempt to cross between those branches.
In other words, it is "very dangerous" to disobey the Forgotten Realms deities. The regime might even punish an inhabitant of Toril for thought crimes if one visits one of the unauthorized locations within the Astral thought scape, that lies beyond the Tree search engine, beyond the control of Forgotten Realms deities.
Direct connections between different planes simply do not exist in Toril's Astral Plane, unless personally created by deities to link their divine domains together. (Meaning, for example, direct connections from any of the Inner Planes to any of the Outer Planes are simply impossible, since no deity can claim those spaces as their domain.)
Of course, the infinity of unsanctioned planes and portals exist in the Astral Plane, but there is almost no way for the inhabitants of Toril to discover them. Toril with its regulated access points are a prison in the mindscape of the Astral Plane.
Conversely, direct connections between all planes can--and often do!--exist regardless of divine intervention in the World Axis and Great Wheel. Indeed, creating such connections is a slow but completely achievable process for purely mortal beings with enough magic mojo.
The Forgotten Realms official Tree search engine, is censorship. The Wheel search engine and the Axis search engine discover and link to places that the Tree refuses to. If someone on Toril got a hold of one of these illegal search engines, one could get to the Astral Sea and explore. But the surveillance by the Forgotton Realms divine dictatorship would probably know about it, especially if using unauthorized usage of the "Weave".
Either these connections exist, or they do not. There could be changing truths, or truths that only apply to area A but not to area B, or truths that apply only in one sense. But these connections between planes can't both exist and not exist in the same world, in the same sense, at the same time.
The rest of the multiverse exists, but the inhabitants on Toril using the Tree search engine cannot access the places that the Tree censors. Even the Astral Plane itself is highly censored by the Tree.
Note that it even (explicitly!) says that plane shift DOES NOT work to get you from Outer Plane A to Outer Plane B!
The Planeshift spell on Toril doesnt work properly. It is like officially censored internet search results.
This is something literally anyone who can cast plane shift can verify. Anyone who can survey the planes can check for counter-examples where a connection not created by deities exists between two non-Material planes.
The Tree, Wheel, and Axis are true. But the Wheel and Axis can easily access websites that the Tree officially removes.