Remove OneDrive „Start back up“ from Explorer

German: „Sicherung starten“ entfernen

1. Open RegEdit
2. Go to HKCU\Software\Microsoft\Windows\CurrentVersion\Explorer\StorageProvider\OneDrive
3. Remove or rename the key StorageProviderKnownFolderSyncInfoSourceFactory

This works instantly, but the key is recreated after reboot. You can prevent this by denying write permissions to the key:

4. In the left pane, right-click on the OneDrive key and then click Permissions. In the dialog click Advanced.
5. Add a new access entry for user Everyone (German „Jeder“) of type Deny. Under Advanced Permissions just select Set Value.

https://superuser.com/questions/1811735/remove-start-back-up-in-file-explorer-new-windows-11-update