Ok so there are good news for Volla 22:
@Bolly from the link you sent me I paste below the message from Jami Kettunen:
"the device page is just about finalized and should be merged soon-ish. and yes the UBports installer does have support to (re)flash Ubuntu Touch on the Volla Phone 22 with support sometime soon also coming to flash SailfishOS or Volla OS as well :)"
And here I paste the answer from Samuel (Volla support) in case it might be useful to somebody else. 🙂
"Ubuntu Touch is NOT the same as Ubuntu Desktop. The Partition size does differ from device to device (depending on the vendor images that will be used) You will be able to use a 256GB SD card for your secondary OS without any issues. Even 64 would be enough.The speed of your secondary OS depends on the speed of your SD card. However, I can barely see any difference between a system that runs on a SD card compared to Volla OS on the EMMC, even when it comes to launching heavy apps on Ubuntu Touch.You will be able to install Volla OS and Ubuntu Touch via the UBports installer."