Small update. After the PRs by @UniSuperBox and @jonius I was finally able to compile the keyboard package onto my phone. In order to accomplish the task I had to slightly modify the command I used before, i.e. crossbuilder with crossbuilder --password=myPro5password because a bunch of commands sent to the phone requires sudo. In this way I was able to get to the end of the crossbuilding process, I believe without errors. At first I changed just a small thing in the code to see the effect on the phone, but then I tried without changing a thing and after a reboot in both cases I got the keyboard not showing up anymore; so I couldn't access the phone because I couldn't insert the unblocking passcode. A fresh UT install did the trick. Any idea why the crossbuilding process seems not working as expected? I don't have the output log this time but, if needed, I can try again to compile and collect a new one.