I missed the most obvious thing too. But I had all this typed!
So if the problem still exists after you move to a supported kernel..
The most useful information is the logs leading up to the freeze. That makes this much easier to track down, since you can filter logs by each boot.
To see your boot IDs, type:
journalctl --list-boots
Boot ID 0 is your current session, still logging entries until you shutdown (or it freezes). If it froze the last time you started your computer, then the boot ID would be -1.
If you remember roughly when it froze, you can find the corresponding boot ID. The --list-boots output shows when each boot started and when the last log entry occurred, so it should be fairly easy to identify.
Once you find that boot ID, use it in the following command (using -1 as an example):
journalctl --boot=-1
# or journalctl -b -1
That will show logs starting from boot. To find where it froze, it’s easier to view them in reverse.
So once you’ve identified where it froze, use something like this (we may as well include more detail by allowing up to INFO level entries):
Also, when copy/pasting (or piping) from journalctl, make sure to use the --no-pager option. (When viewing logs, omit it.)
journalctl --boot=-1 --reverse --priority 6 --no-pager
# journalctl -b -1 -r -p6 --no-pager
Find where the freeze occurs, then paste the logs leading up to it. They’re timestamped, so include everything around that time and post it here.