After the boot fails, grab your USB and boot up the live environment. Use the chroot tool, or use garuda-chroot as described here to get into the non-booting system and from there you can pull up the journal from the failed boot.
An easy way to get the journal uploaded to the forum would be to pipe it to termbin:
journalctl -b -1 | tb
or
journalctl -b -1 | nc termbin.com 9999
Make sure the system is internet connected of course. 
Then, just plop the URL right here in the thread so we can take a peek.