I also recently encountered this.
It appears that there's been an update which reverts to the earlier
version of OpenSceneGraph, but at the time of writing it's still
awaiting a release, according to the package tracker:
https://tracker.debian.org/pkg/openmw
As a workaround, since the only change in the most recently released
version appears to have been the OpenSceneGraph dependency, one can get
the previous version of the packages (0.45.0-3) from the Debian snapshot
archive:
http://snapshot.debian.org/archive/debian/20190709T210115Z/pool/contrib/o/openmw/
I downloaded and manually installed (dpkg -i) the packages from there,
and have been playing with that version for the past few days without issue.
--
Mel
