@Imogeeen Please reinstall all the expansion packs you uninstalled earlier. If you don't want to use them going forward, there are ways to stop them from loading; just let me know whether you have a disc or Steam install. For now though, the packs' registry entries were probably not removed, and their continuing presence can and does cause the service initialization error.
If that doesn't help, uninstall Sims 3 using Revo Uninstaller (the free version is fine), and reinstall only the packs you want to use. You'll need to apply the Alder Lake patch or another workaround again, of course.
McAfee is usually not a problem for Sims 3, but if you want to be thorough and potentially save yourself a troubleshooting step, disable real-time scanning while reinstalling Sims 3, that is if you need to reinstall. Test the game once before reenabling scanning. As long as you don't do anything else at the same time, your computer should be safe.