@magnargj See also this topic that I just created:

https://forums.ubports.com/topic/10388/volla-phone-22-replacing-a-broken-display

I contacted Volla directly via their website's contact form and they offered to sell me a screen. Though I'm now waiting for roughly a week for them to reply to my last email, following up on my request to actually place the order.

Also I asked in one of the shops that are listed as Gigaset service partners here:

https://phone-service.de/gigaset/

and they appear to be able to repair the Volla 22 phone, as that is the same (?) hardware as the Gigaset GS5. Though there is still the question whether the latest ubports firmware is recent enough to support the newer screens which appear to require newer driver support compared to the stock screens (see the new thread that I linked above).