Hello! We've added more diagnostics to the latest beta version of the launcher - it should now generate a launcher_log.txt file if you try it. Could you please try that and attach the resulting launcher_log.txt file?
Looks like whatever you did in 2.1.5908 resolved the startup issue, as the launcher fully starts up and works as expected. Here's the launcher_log.txt from after upgrading.
MCL-11523
Hello! We've added more diagnostics to the latest beta version of the launcher - it should now generate a launcher_log.txt file if you try it. Could you please try that and attach the resulting launcher_log.txt file?
Downloads:
https://launcher.mojang.com/download/Minecraft-beta.deb
https://launcher.mojang.com/download/Minecraft-beta.tar.gz