Thank you for your posts.
Cubasis does work with iPadOS 16.3
The solution is to make sure the internal soundcard is set to on
Even though the iPad will not use this with an external soundcard.
I now have Cubasis working very happily with IpadOS 16.3 and my UR44
( It also works with my XR18 - however, due to another non audio problem - the wifi and the XR editor are presently conflicted )