I've figured it out! In my Pictures folder, there were folders plus a few random photos. By moving folders and pictures back in in groups, and if a group failed, taking out half that group, I narrowed it down to these two photos. These are OOTC JPGs from my Canon RP, except I used some program (probably GIMP) to crop them, then saved as I often due to edits with the original IMG name followed by "cropped". One of them is labeled "cropped 2" but it's just a copy of the first, so I don't know why I have it.
I have NO idea why a simple cropped JPG would cause DPP to crash on startup, but that's what my issue was! I tried renaming the photo, removing IMG and naming it test, no luck. Still crashes DPP if it's in the folder DPP is looking at.
Doesn't matter WHERE the photos are either. I left the photos in the temp folder in my Documents folder, started DPP, navigated within DPP to the folder containing the two pictures, and it immediately crashed. So there's something specific to these particular images that DPP just does not like. They open fine in GIMP, IrfanView, Photos, Paint, Paint 3D, and Snip and Sketch. So it's not like they are corrupted files. DPP just hates them for some reason.
If anyone is super curious, I can put the actual file into my Google drive and link it here for downloading if you want to see if it crashes your copy of DPP.