Can't launch the game "Service initialization failed"

I gave that a try but it didn't work, got the same problem in my new local account :( 
Feels like I've tried everything I could find on here that worked for others but nothing seems to work for me. The game ran flawlessly a couple of days ago. 

I saw a suggestion to do a dxdiag earlier, so I did that if that can be of any help? 

d0fdef48c2338f24  Your dxdiag shows that a component of McAfee is crashing, and it's possible McAfee is blocking Sims 3 from starting, especially since there are no Sims 3 errors in the dxdiag.  (No errors typically means that the program is blocked rather than crashing.)

Because McAfee is crashing, I would suggest uninstalling and reinstalling it.  Here's how to remove it:

https://www.mcafee.com/support/s/article/000001616?language=en_US

Since you're uninstalling anyway, it's worth testing Sims 3 before reinstalling.  Clear the EA App's cache, again, if you have already, and repair the game (Sims 3 > Manage > Repair), then try to play.

https://help.ea.com/en-us/help/faq/clear-cache-to-fix-problems-with-your-games/

I'd suggest testing in the new account if the main one doesn't work.  It's kind of overkill to try uninstalling and reinstalling, but if you want to know you did everything, try it, still with McAfee gone and using another new folder in case McAfee changed the permissions on the folder you previously used.  As long as you don't do anything else at the same time, your computer will be safe.

If and when you do reinstall McAfee, and I'm not making that decision for you, be sure to set exceptions for EADesktop.exe, TS3.exe, and Sims3Launcher.exe before you try to launch the game again.  As far as your antivirus is concerned, you don't necessarily need anything more powerful than Windows Defender, which works very well these days without blocking the programs you might actually want.  But it's your call.

That makes sense. I have uninstalled McAfee both with the standard Windows-method described in the link you sent, and via MCPR. I then tried clearing the cache and repaired the game and then launching the game with the same error code as before... I did this in the new local profile I created yesterday. Tried in my main one too but same result of course. I tried uninstalling and re-installing in my local account in a new folder at C:/ - no luck. 

I didn't try uninstalling McAffee as an advanced user (third step described in the link you sent) because I tried searching everywhere on the computer and can't find any trace of any McAfee-files left. Tried Revo too. Is it possible some McAfee file is still hiding somewhere and causing problems? I have no intention of re-installing it, it came with the computer and I haven't had any subscription since the free trial expired. 

Ran a new dxdiag, does it say anything different? 

d0fdef48c2338f24  The new dxdiag doesn't list any new Windows errors.  And McAfee, like any antivirus, can leave behind unwanted effects, for example changing permissions on folders.  But it can't have new effects if it's not running, and you should be able to see any running program or process in the Task Manager.  So it shouldn't be affecting things now.

What I would suggest here is uninstalling again and manually searching the entire registry for any entries with Sims in their names.  Don't delete anything that belongs to another Sims game you have installed, just Sims 3, and of course don't do this with the game still installed.  Revo is normally reliable in this regard, but I do remember another recent example of it not finding some leftover registry entries that the player then needed to remove another way.

To access the registry, click Windows key-R and enter regedit in the run box.  Before doing anything else, click File > Export, and export a copy of the entire registry just in case you delete something critical and need to restore it.  Save the file to your desktop or somewhere else easily accessible.  And please keep in mind that this is a snapshot of the registry, and thus its usefulness will expire once you install something new that creates its own entries.

When you have your backup, you can search for Sims and see what you get.  Everything Sims 3-related should be under WOW6432Node, as the game is a 32-bit app.  If you're not sure what you're looking at, feel free to list any questionable entries.  It would be best not to post screenshots of all the values on the right though, as some of these are specific to your computer.  The names are fine, just not the values.

When you're done, that is if you're not asking me about any particular entries you find, I would suggest running a repair install of Windows just to be thorough.  Here's how (option two):

https://www.elevenforum.com/t/repair-install-windows-11-with-an-in-place-upgrade.418/

The process is relatively quick and shouldn't delete any of your data, but if you get to step 14 and are NOT asked to keep personal files and apps, back out and start over.

I did a manual uninstall and searched regedit for files and found a few left that I removed. Then I did the repair install of windows and installed the game again - same error message. I installed it on my local user.

However, when I tried to launch the game I got an error message from Windows Defender that I never got before, it says that it had blocked the app - "your administrator has blocked this action" and that it's the controlled folder access that blocked it even though I have added TS3.exe as an allowed app. I hope I translated the message, english is not my native language. 

Any ideas? Or should I just re-install the whole computer? I don't have alot on it so it wouldn't be that hard for me to do if there's no other solutions, feels like we've tried everything at this point...  

Just adding that I have allowed the nessecary .exe-files for the Sims as exeptions since before, and I also tried turning off controlled folder access but it didn't work. 

d0fdef48c2338f24  Did you make the new user account an admin account?  It would start out without admin permissions by default, which would also prevent you from making some changes and might tighten the security for Windows Defender.

It's also worth repairing the game after changing Defender's settings.  Doing so would put back any files that were quarantined and that the game might not be able to run without.  And not only would you need to set an exception for TS3.exe, you'd need ones for Sims3Launcher.exe and EADesktop.exe as well.

If that's not the issue, we could continue to troubleshoot, but in all honesty, reinstalling Windows would likely be the fastest approach here as long as it's not too inconvenient.  I will keep trying to help for as long as you like; I'm just saying you might find that reinstalling Windows is a better use of your time.

Yes, the new user is an admin account and I included both Sims3Launcher.exe and EADesktop.exe in the exeptions. 

I'm going to reinstall Windows, I feel like it's useless to keep troubleshooting when nothing has worked so far. 
Thank you so much for your help and patience, I really appreciate it :-) 

So I reinstalled my computer and the Sims - and I STILL get the same error message 😅
I don't know if I should laugh or cry at this point. 

d0fdef48c2338f24  In the new Windows install, do you have any special characters in your username?  Is OneDrive running now?  (It shouldn't cause this particular issue, but it doesn't hurt to ask.)  Did you install anything at all aside from the EA App and Sims 3, or did an antivirus install on its own, perhaps one that came with the original computer?

Please also let me know what country you're in and whether you use a VPN.  Neither of these should trigger this error either, but you've addressed almost everything else.

Finally, do you have access to another computer where you could install the game as a test?  This error isn't typically account-related, but stranger things have happened.