grafi, according to this post,
Upgrade Rock/5.0 to Rock/6.0 (April 23, 2025) - #2 by grafi
you downloaded the ISO from the ABF days before the announcement. It did not come from the download button on the https://www.openmandriva.org/ page. Granted, you may not have known it was testing, but you installed it. You even stripped Plasma out of it and replaced it with XFCE.
Hopefully, you got it all sorted out now. If not, just ask for some help. We will be glad to give you a hand.
EDIT:
I will see if there is a way to get a note on the ABF Product Build Lists page stating that this is not the approved download area and builds placed here are testing and may or may not fail. We had no way to know that you did not want to help with the testing of this ISO.