We are trying to upgrade our RHEL servers and found that documentation does not show 8.9 as being supported.
DLP16.0RU1
At the time of the release of 16.0RU1, RHEL 8.9 had not yet been released.
RHEL 8.9 has been tested, certified and is now supported as of DLP 16.0.2.
Red Hat Enterprise Linux 8.0, 8.3 through 8.4, 8.6, 8.8, and 8.9
Reference: 16.0.2 System Requirements