Further reading and I learn that DX12 with Nvidia Filters and Frame Generation causes CTD. One thread says that either DX12 with Filters or DX12 with Frame Generation will work but not DX12 +Filters+Frame Generation.
My options is not showing Frame Generation option when using DX12 so I’m guessing it’s not set up for it in the BIOS. Anyway, I was still getting CTD with DX12, so there are other issues that can cause the CTD with DX12.
I did go into Nvidia Experience and noted that my settings were not optimized for MSFS according to Nvidia Experience. I had it automatically adjust the settings for optimization and then ran the sim in DX12 for a full flight without a CTD. I did start the sim through Nvidia Experience after it optimized it rather than starting it with the FSUIPC app, but don’t know why that would matter.
Not sure if any of that corrected whatever the problem was with DX12, but I’m going to run DX12 until I get another CTD. If none - great, but if I get more CTD I’ll just go back to DX11 because I’m really not seeing much difference between DX11 and DX12.