That RAW you quote is part of the play loop saying that combat is turn based. That doesn't make it not part of the play loop. So, yeah, I disagree with your assertion.
No, it does not, it says: "In certain situations, particularly combat, the action is more structured and the players (and DM) do take turns choosing and resolving actions."
So no, not only combat.
Not so "obviously". When the DM describes the actions of a monster/NPC, they are describing the environment.
No, sorry, this is not the environment, this is the example of the environment: "how many doors lead out of a room, what’s on a table, who’s in the tavern, and so on."
Over to the player(s) - granted ever so briefly - to see if they have anything they can do in response - and then the NPC/monster's (and PC's reaction, if there was one) are resolved. Back to step 1.
Are you saying that is not happening?
No, because actions by other people are not "the environment", this is a bizarre understanding of the term.
Before the player's turn, the DM can narrate the state of the combat (step 1) then ask the player what they want to do. The player describes what they want their PC to do (step 2) and then the actions are adjudicated (step 3).
No, this is not what the RAW says, once more: "In certain situations, particularly combat, the action is more structured and the players (and DM) do take turns choosing and resolving actions."
It clearly shows that while in some situations the PCs actions are what matters and is resolved, in others, and in particular combat, the actions choosing and description also obviously concerns NPCs and Monsters, chosen by the DM.
Structure does not override the play loop. Although it can certainly speed it up. It's still happening and I actually find it helpful to think of it that way.
That might be your way to consider it, but it's not what the RAW says.
Quickly narrating the state of the environment before every player's turn has become a standard operating procedure for me as DM over the last year and a half or so, and our game has benefitted from it.
As you say "the state of the environment". Now, personally, I prefer a more active game where NPCs take actions (chosen by the DM) independently of what the PCs do. And this is clearly supported and encouraged by RAW, particularly in combat but not only.
It's actually a broader reading of the loop.
It's also a very selective reading of the loop, a very unusual reading of what an environment means, and specifically not reading sentences in the same section which prove without doubt that the PCs are not the only ones choosing actions, and not only in combat.