I had edited for length, but I did already try clearing Edge's browser cache, both for 24 hours and for all time, and it did not fix the login issue. Being on Windows 11 I don't have and can't download Internet Explorer, and I already spent so much time trying to get everything working in my game that I decided not to mess around with Firefox. That would mess up a bunch of other logins etc. that would cost me even more time to fix. Plus I'm pretty sure it wouldn't do anything since the game launcher is supposedly tied to IE/Edge, so in theory it shouldn't be tied to Firefox.
As for installing to a different drive: I already was installing on a different drive from my OS and not in Program Files, so there was no extra step there. I might return and attempt the Revo fix.
As far as saves etc. I'd already deleted all of them because I was trying to run some mods (mostly Nraas) to make the game run smoother. And no, I did not have them installed at the time of the glitch singularity. I'd already removed the mod folder at the first sign of trouble.
I don't know which expansions/packs installed and which didn't, I just know that it refused to download a certain stuff pack. I think there were more expansions and stuff packs it had not installed, but I wasn't paying attention to what had and hadn't because, I didn't expect to have any problems. And, when I did, I thought it would resume download as normal afterward, and canceled when it didn't without thinking to note which specific pack it was. In hindsight, I might've been able to restore my old Sims 3 folder and not have the login issue as well, except I'd already deleted it assuming that all would be well once it repopulated into my Documents folder. So that part is on me, but the glitch itself is not.
Most likely I'll just have to wait it out until whatever cache the data is saved in is cleared, and that'll be months or a year from now, plus it doesn't guarantee whatsoever that I'll be able to install my content again. I tried multiple times, installing it all straight from the Store and deleting duplicates so it didn't double or triple install. Not once did it show up in game, either logged in or offline mode.
It's not that the game is unplayable in the state it's in, but I paid for all this content and it shouldn't be unplayable now. What's the point in buying new settings for the game to play in, if you can't use them? What's the point in having stuff packs and expansions if they won't even download? Plus, of course I can't even try anything else at all to get my store content working if the login doesn't work. I just hope I can get my game running again before the eventual inevitable retirement of the Sims 3 store, when I won't be able to access my content anymore--since the EA app does not recognize that I own it, after all.