Re: Sims 3 launcher running in tray while playing.
@172e3cda00349872 @TrexterZiam How about an even better workaround?
But first, a disclaimer: This approach worked well for me—I could login, load, and save, with no apparent ill effects. However, I never tried to download or install any store or custom content, nor did I export or upload anything of my own. I also tested on a throwaway game folder, and I suggest that anyone else trying this out do the same, or at the very least keep a backup of your existing game folder until you're satisfied with the results.
Again, the issues with the launcher running in the tray and claiming to be uploading when closed out can both be remedied by removing the Sims3Logs file from the TS3 game folder in Documents. (As @172e3cda00349872 has mentioned, the Sims3LauncherLogFile may also be involved, although this has not been the case for me in particular.) But even better, the files' properties can be changed in a way that disallows whatever nonsense has been going on with the launcher. The path is:
Right-click on the affected file, Properties > Security (second tab) > Edit; highlight "Admin" and check the box to deny "read"
This was enough to make the launcher behave as normal on my Windows 10 setup, but if it's necessary to go further, checking all the "deny" boxes for Admin, System, and <username> appears to have no negative effects on the game. And this change can be undone just as easily, simply by unchecking the boxes again.
Special thanks to @igazor for his insight. I don't want to make him uncomfortable by gushing all over this thread, so I'll just say that we all know he's wonderful.