@PurplePlumbob I haven't seen any other reports of this today, so I don't think it's an EA-side issue. Instead, it's likely your computer or your connection. For the latter, disable your VPN if you use one, and otherwise, try a different network if you can. For example, you could set your phone as a mobile hotspot, using data rather than your home wifi, and connect to that, provided your computer also has wifi.
If this doesn't help, create a new admin Windows account and see whether the launcher loads properly there. Make the account local, as in, don't link it to your Microsoft account. This is to test whether the problem is limited to your current account or more global.
Thank you so much for your advice. I disabled my VPN and used my mobile hotspot, but the launcher still wasn't letting me log in. Strangely, it took me resetting my Google Chrome account and restarting my laptop for the problem to be resolved. Go figure. I'm just glad that it's working now!
Update: the problem returned. I took your advice and created a new Windows account. I made sure that the account wasn't linked to Microsoft, and launched the game. The launcher worked perfectly. I was able to log in with no difficulties, which I'm guessing means that my Microsoft account is the source of the problem. Where do I go from here? Microsoft Edge is not my default browser, and I've already reset it quite a few times. Any further advice would be much appreciated. You've already been a huge help, so thank you for that.
@PurplePlumbob You could try setting your default browser to Edge, just temporarily and to see whether it helps. It shouldn't matter, but then you've already demonstrated that Chrome is at least partly to blame here.
The fact that the launcher works in the new account makes it clear that the problem is in the main account, but it can often be difficult to find the problem, whether it's a user setting or a permissions issue or something else entirely.
I tried making Microsoft Edge my default browser, but no dice. At this point, I've tried signing in and out of all of my Microsoft accounts, tinkering with the advanced settings and resetting both Chrome and Edge several times. I'm at a bit of a loss right now. The only thing I remember altering between now and when my game was last working was the Microsoft Authenticator app. However, I've since reverted the change I made back to how it was before, and still no luck. I'm going to start delving into my custom content to see if something's wrong there. It's a long shot, but it's worth a try at this point.
Edit: The only other thing to note is that I began receiving a lot of script errors around the time that this problem arose. Could that have anything to do with it?
@PurplePlumbob Scripterrors would have nothing to do with this problem. The errors are entirely based on what's happening in the running game, and the mods that generate them have no effect on or access to the launcher data that isn't working for you.
I don't really know what to tell you here, unfortunately. You could try running the takeown command on Documents, on the off chance that this is a permissions issue, but I don't think it is. See this for more details:
https://answers.ea.com/t5/PC/CURRENT-ISSUE-Sims-4-already-running/m-p/13276380#permissions
Aside from that, I would suggest simply keeping the secondary account for when you need it, and otherwise not signing into the launcher or game. You're not missing much by skipping this step, only some badges and access to Simport.
