@HistoPol@smallcircles To be honest I have no idea if Threema will work? I don't use android anyone since few years. Btw.. This app is open source or not?
I think better solution in such case can be Session, SimpleX, or something similar to them both. They can be normally used on for example SailfishOS with android api enabled. They also have a cli and desktop versions as well for many operating systems.