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."

@kugiigi Thank you for the answer! I did it following your instructions and it came back!
Yeah Volla 22 has the multiboot option where Volla OS runs in the internal storage and any other OS on the SD.
I'm anyway considering installing only Ubuntu Touch as I'm not a fan of android.
The only thing is that Volla 22 isn't listed among the supported devices but I know you can buy it with Ubuntu Touch installed as only OS plus from Ubuntu desktop there's the option to intall in on Volla 22 from the UB Ports application so I should probably go for it.
I'm very happy to finally have ubuntu on the phone! I've been waiting years for this moment! When Canonical abandoned the project it was a terrible news.