Upgrade from OC to NC 12.0.3 not possible?

I had OC and want to switch to NC. So I took the latest version and according to https://nextcloud.com/migration/ it should work.

I choose the manual path. First deleted all OC files (except config and data) and then copied the new NC files. And started sudo -u www-data php occ upgrade. But I get this:
Exception: Updates between multiple major versions and downgrades are unsupported.
Update failed

What can I do?