Did a fresh Rocky 9 installation, result was the same as after the previous 9 install, no volumes on the array visible (but the array was active). The remark of @jlehtone triggered me and this did the trick :
$ lvmdevices --adddev /dev/md0
$ vgchange -ay vg-datastore
After this, the volumes became visible ant mountable!
Is this what we can expect after a fresh install, or should the volumes be ready like after the Rocky 8 installation?