Persistent error: "Invalid Login Information. Please try again." - 64-bit SIMS 3

@julijaforest  Please try changing your password to something with only letters and numbers, no special characters, accents, etc.  Clear your browser caches again and then try to login.

If that doesn't help, open Documents > Electronic Arts > The Sims 3 > Downloads, and delete the file labeled [your email].bin, then try again.

@julijaforest  Did you repair the game after running the Origin reset tool or otherwise clearing its cache?  The repair puts back files that are removed with the reset tool and that are involved in authenticating your install, although so far I've only heard of this affecting store and custom content.  Store stuff uses the same authentication as the in-game logins shough.

Otherwise, do you have two-factor authentication enabled in your account?  It shouldn't matter, but perhaps it's interfering; you could disable it temporarily to test.  (Clear your browser caches again afterwards.)

If that doesn't help either, as a test, please try signing in and running the game from a new admin user account on your Mac.  That can help distinguish between user settings and other issues.

@julijaforest  Try using your phone as a hotspot, at least long enough to sign into Origin and try to login to the game.  Make sure the phone is using data, not your home wifi.

If that doesn't help, what happens if you try to play while your computer is completely offline?  You can sign into Origin and put it in offline mode, then disable wifi before pressing Play.  I'm curious whether you're able to load a save or start a new one.  If you can't do either, please move your entire Sims 3 folder out of Documents > Electronic Arts and onto your desktop, then repeat the above.  Your saves and other content will be intact in the folder you've moved but temporarily not read by the game; you can put your content back later.

@puzzlezaddictThanks again for replying!
So here are my findings:
The first suggestion did not work, unfortunately. I got the same error at login. Then, I attempted to launch the game - the issue is the same on my home wifi as it is on my mobile hotspot.

The second method the first time did not work.
The second time I tried it, however, it was able to load up my saved game and it launched successfully to the final loading screen. But, at 30% of the bar left, the game crashed entirely. I got the crash error script by Mac for this situation.

The third suggestion playing offline with the Sims 3 folder moved to Desktop worked. Though containing the usual bugs and some visual glitches of the 64-bit version, it worked. Perhaps it suggests problems in my moved Sims 3 folder?

@julijaforest  That may well be the case.  You can try playing while online using the new Sims 3 folder, with and without signing in.  If the game stops working again, it's no big loss; you can just create another clean folder.

When you're done experimenting, you can move your saves from the old Sims 3 folder to the new one, as well as any other content you'd like to keep.  If you're using mods and/or custom content, it's better to test it in the new folder first though, in case the content is causing any issues.

@puzzlezaddict So my experimentations have been fruitless so far. Once I launch the "new" blank game, I am still not able to log in to my account (both on my home wifi and mobile data).
After logging in with my credentials, I get stuck on the same screen as before. I know that I could play without logging in, or just with the base game, but at this point, I am determined to get my game back to normal. Of course, it is preferred to play with my Sims 3 store content and all the fun things it provides, but now I am not able to.
I still have a feeling that it could be a question of the compatibility of the new macOS update (Big Sur) with the not-yet-patched 64-bit version of The Sims 3. But I am not sure.

@julijaforest  I never login and can always use my store content.  What happens when you try?  If it's a question of installing, you can download directly from the store instead, without needing to login to the launcher.  Or at least you should be able to.  A few players report that this doesn't work for them, no idea why, but it does work for me in a couple different versions of macOS.

As for whether the login issue is related to Big Sur, it's possible.  However, I haven't seen any other reports of this issue recently from players with Macs.  And judging from the other threads here, there are plenty of players running Big Sur; I'd expect at least a few of them to also use the in-game sign-ins.

One thing I didn't ask, but it's worth mentioning, is whether the account you can't sign into is the same as the Origin account that downloaded the game.  If not, store content won't work, and online logins may not either.