I think Crawford’s answer was both clear and accurate. There is an official D&D setting, and it is “the multiverse.” This is similar to Magic: the Gathering where all the various planes that may be the focus of one set or another exist within a unified meta-setting, also called “the multiverse.”* All the different D&D settings exist within this meta-setting, which has certain baseline assumptions, such as the great wheel cosmology and D&D’s magic system.** The Forgotten Realms is just one setting among many that exists within the official meta-setting. It’s no more “default” than Dominaria is the “default” plane in Magic: the Gathering. Which is to say, yes, it holds a significant place within official canon, due to being the focal point of a majority of the official material, especially early on in the brand’s life cycle.
But that’s kind of circumstantial. It could easily change, especially if there is a lot of consumer demand for canon material focusing on other settings. We saw that happen with Magic, where WotC tested the waters first with a block set in Otaria (which is on Dominaria but is nonetheless pretty distinct from what they had been doing up until then), then branching out into more different settings, and at this point Ravnica is practically an equally prevalent plane in Magic canon to Dominaria. We’re starting to see them do the same thing with D&D, where they tested the waters with Eberron, and now it looks like they’re going to continue releasing material for other settings. With the success of Wildemount, who knows, Exandria could end up becoming the Ravnica to Aber-Toril’s Dominaria.
All that said, I don’t think WotC has any plans to “move on” from the Forgotten Realms any time soon. Mearls’ answer gives a great explanation of the value of having a setting that they can lean so heavily on, and I doubt they’re eager to lose those advantages. For these reasons, I voted for “friends with benefits.” Forgotten Realms isn’t the official setting. It’s sort of functionally the “default” setting for the time being, but only in the sense that they’ve been focusing heavily on it, there’s no reason they can’t or won’t shift that focus if they think the benefits of doing so will outweigh the costs. Even if that happens though (and I do think we’re starting to see it happen,) that won’t be “Moving On.” Forgotten Realms will probably always hold a special position in D&D canon, just as Dominaria still holds a special position in Magic canon, and sets that focus on it are always treated as big, special events and play hard on longtime fans’ nostalgia.
*and with the various Planeshift documents and Guildmaster’s Guide to Ravnica, they are arguably the same meta-setting, at least in D&D canon if not in Magic canon.
**This of course calls the unity of D&D’s multiverse and Magic’s multiverse into question, since they have different cosmological assumptions and different hard magic systems. But YMMV on how much that really matters to you. And anyway, there are other official D&D settings that bend or even break these assumptions. The current approach seems to be to handwave these setting inconsistencies with some vague mysticbabble, and fair enough if you ask me.