@nlwitje What regedit trick did you use? I'd like to know both what category you edited and what the new value is.
And just in case you don't already know, installing the game on a different drive does not move the location of the Sims 4 user folder. That will always be in Documents > Electronic Arts by default. If you want this folder elsewhere, you'd either need to move the location of Documents (which can be done through a registry edit, so maybe you did this already; but there's an easier and less risky way), or you'd need to create a symbolic link to tell the game where to look. For the latter, please see this guide:
https://crinrict.com/blog/2020/02/moving-windows-documents-folder-to-external-drive-via-symbolic-link.html