Leliel2000 It's likely that some of the registry entries for the game are missing. Depending on which ones are gone, that could explain why the game doesn't show in the Windows Control Panel and why the EA App can't uninstall it. The "service initialization" error is also usually related to missing registry entries.
So please try to uninstall Sims 3 with Revo Uninstaller (the free version is fine). Here's how:
[Read First] Running Sims 3 in Windows | EA Forums - 8323446
If Revo can't find the game, you can manually delete it and then use Piriform's CCleaner (the free version is also fine) to clean the registry. Make sure the EA App is closed and the EABackgroundService is NOT running in the Task Manager, in the background processes list. Simply delete the Sims 3 folder wherever it's installed; you can see that in the EA App, under Sims 3 > Manage > View properties.
After deleting the folder, empty the recycle bin and restart your computer before using CCleaner. You can search for entries with sims in their name and flush everything that's Sims 3-related. Then restart again, clear the EA App's cache, install the game, and see whether it works. As with Revo, I would suggest installing into a different folder, one you create for this specific purpose.
https://help.ea.com/en-us/help/faq/clear-cache-to-fix-problems-with-your-games/