Following a failed site upgrade from 1912 to 2203 all Delivery Controllers and the site database were rolled back to a pre-upgrade state.
This resulted in the following error in Studio:
"This version of Studio cannot be used to upgrade your Site. Use the same version as an upgraded Delivery Controller."
Investigation revealed that one of the DDCs remained with version 2203 and this corrupted the restored 1912 db. Even after restoring this DDC to 1912 like all the others the error remained.