It's been about 80 hours, no lockups. My issue must have been some type of driver conflict with the 21.3, or something internal to 21.3 that just conflicted with my hardware setup. LM 21.2 has been actively running with all the same software (except for whatever would be locked to the 21.2 repositories)... all the same hardware.
I've even updated the Nvidia drivers to 535 and Linux kernel to 6.5 (as previously in this post when I was troubleshooting 21.3). I chose to upgrade these because I was having the lockup issue prior to these two updates, so I thought I'd try them on 21.2 to see if they cause any kind of trouble... but they have not. I hope if someone else runs into the issue that maybe something I've posted here helps them... unfortunately, I don't have any root cause for this issue.
Linux Mint 21.3 Repeated lockups after upgrade from 21.2
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Re: Linux Mint 21.3 Repeated lockups after upgrade from 21.2
Except there are no drivers which changed. All the changes (kernel, nvidia, etc.) you now have installed. Both versions are based on Ubuntu 22.04 so the drivers are the same.
Here are the New Features: Linux Mint 21.3. I have no guesses what the issue might be unless something happened in the upgrade process that didn't fully upgrade properly but was not an obvious problem. It wouldn't be the first time something like that happened.
A woman typing on a laptop with LM20.3 Cinnamon.