I am not certain yet, but I may have fixed it.

I first did a complete a total uninstall of the game. I then deleted the game files in My Documents on my second HDD.
Then, I disabled my second HDD, and attempted to reinstall.
I got an error that said the Documents folder didn't have 2gb of space. This was indicating to me that the game was looking for a documents folder that couldn't be found. I realize it's because my PC was telling it to find the Documents folder on the disabled hard drive.
Re-creating the Documents folder on the C drive manually didn't work, so I followed these instructions to edit my registry. https://www.thewindowsclub.com/cant-...-same-location
OneDrive was still wreaking havoc because it really wanted that Documents folder to be on my D drive. So I uninstalled OneDrive, and the FFXIV install started.
Booted up for about 5 hours today, with zero crashes.

So now, I need to slowly start reintroducing things to see if it starts to crash again. I played for several hours today with zero crashes, and will attempt some more tomorrow. If that works I'll take these reintroduction steps

Boot PC and let Antivirus and other background processes start. If no crashes...
Re-enable Hard Drive. If no crashes...
Reinstall OneDrive - and make sure it doesn't F with the Documents folder in it's new location.

It will probably take me several days of doing those 1 at a time and putting in the playtime to install confidence that it' fixed, but early signs are good.