I was reading Red Hat docs on this issue, it does say CentOS, but nothing on CentOS Stream.
Stream is not supported in convert2RHEL yet, but we are working on it.
There are no fundamental blockers, rather couple of differences:
One is cosmetic, as we need to adjust some code which does parsing of OS names to accommodate for Stream.
The other is more interesting: we need to deal with possible downgrades.
As CentOS Stream is slightly ahead of RHEL the conversion can be done in two ways: 1) you would freeze your current Stream system, wait for RHEL to catch up, and then do the conversion to a newer RHEL or 2) you would allow conversion with downgrade.
The first path is easier to implement, but we are still considering options.