Win11 desktop client: "Some data couldn't be synced" with "couldn't open sync database"

[GAPPSRefusenik]

I was suffering from the same error, and this solution completely cured it for me:

Unable to sync Documents or Pictures folders from Desktop Client (Windows 10)

This is an old post, but while running the Windows client 3.13.0, I ran into this same error. I thought I’d share the fix I found in case anyone else comes across this post with this issue. My setup is simplified. This is a local folder on a non-root local drive, but trying to sync it to my Nextcloud server. I kept getting this same error AFTER the initial sync worked. I hadn’t changed a thing, except a recent upgrade to the client. So, after some testing and comparing the permissions with th…