Yep. I've tried to do some research on the error (Could not find or load main class net.minecraft.client.main.Main) but all I could find was issues related to Java or a corrupted download of the game. Not really helpful.
EDIT: maybe something useful there: https://www.raspberrypi.org/forums/viewtopic.php?p=1045520
It's about an older version but you can check anyway: start the launcher, edit profile and check what version is in "use version". Eventually try several choices and be sure that options about snapshots/beta/alpha versions are unchecked.
BTW, do you remember which version you had on Raspbian? It's possible that the latest one can't run on the Pi for some reason (even on Raspbian). If you remember, try to set the same one on Ubuntu MATE if possible, to see if it runs. If that's the case, from there, you can start checking newer versions.
There are potential other solutions in the thread, someone is talking about an alternative launcher, replacing libs and so on. I haven't read the whole thread but it might be a good idea.