Thank you @rodinux ,
finally I’m now running YNH 11 with pq 13, too.
But since I used other apps that needs postgresql, it didn’t go that easy.
I did, what you told me, but that crashed my Invidious, Mastodon, Moodle, Peertube, Pixelfed, Pleroma and Synapse.
So after some fiddeling I ended with uninstalling all of them, purging postgresql* and then restoring the apps from backup. Well, it took me some hours but now everything is running fine again.
Thank you.