Re: I can't change settings
@D1NACALIENTE It sounds very much like the game can't write to the Options.ini file, which is in Documents > Electronic Arts > The Sims 3 and stores all in-game settings. The question is why. Is OneDrive running on this computer? If so, it could be a problem whether you deliberately use it or not. Try pausing syncing, which you can do by right-clicking the cloud icon in the lower-right corner of the screen.
If this doesn't help, or OneDrive isn't running, do you use a third-party antivirus, and does disabling it (temporarily) help? You'd only need to run a quick test, and with nothing else open on your computer at the time, this wouldn't be a security risk. Windows Defender shouldn't be a problem here, but you could try temporarily disabling Controlled Folder Access as well.
If neither of these is relevant, try removing the Options.ini file to let the game generate a new one. Let me know if you can't, whether you get an error or the file simply sticks around; otherwise, you'd need to redo all your in-game settings, but at least you'd know whether that was possible with a fresh copy of the file.
Please don't use any compatibility mode for Sims 3. The game runs fine in Windows 10, and compatibility modes can make troubleshooting more complicated.