Hi and welcome to Nethserver Community.
Nextcloud doesn’t support upgrading multiple major versions, so you’d need to update like NC28 → NC29 → NC30 etc.
The recommended way is to update via Software Center which provides one update after the other.
I don’t provide Nextcloud in my repository, I guess you updated from CLI?
Here’s a similar issue which was solved, basically you need to install the right version to make the upgrade work:
Please create a backup/snapshot before trying to solve the issue by upgrading/downgrading Nextcloud as it’s not supported and could lead to errors.