Looks like this is a duplicate of
- Rename local Nextcloud folder - #3 by MarkusT
- Renaming shared folder / update problem - #13 by floatingpurr
I had the same issue and solved it by just changing the NextCloud config file to the new path.
In Linux it is the following file: $HOME/.config/Nextcloud/nextcloud.cfg
In the [Accounts] section all synced accounts are listed. If you found the sync entry you can just change e.g. 0\Folders\2\localPath to the new path.
This worked well for me. Just make sure to stop the desktop client before you modify the config file.