I wish I knew, LOL. Two years ago the 5D MKIV was on sale and I decided to buy a new one. At my age that was a mistake. I have a number of Canon bodies, as well as 5D, 5D MkII and the Mk IV is so much different, both in physical controls and software, that the learning curve is very high, at least for me, now. I just turned 76
About all I can suggest is Google up the various models and compare features.
If you have a pretty good DSLR you can Google up the "vs" and compare, that way you can compare what you know, like this EG:
https://cameradecision.com/compare/Canon-EOS-R5-vs-Canon-EOS-5D-Mark-IV
On a side note, I also have an M50 which I guess stands for "Miniature" and can be used with adapter with EF lenses. I found out accidently that it is for all intents, a miniature "R" with a different mount.
Mine so far as I can remember LOLOL
XT/ 350D, 40D a pair, 7D several, 5D, 5DMkII, 5DMkIV, SL-1, T6, T something I can't remember LOL, at least 2 Elan series film, I've forgotten?? film EOS 5 and 7 and maybe a 3.
EFS several, and EFS17-55 2.8, EF 50 1.4, EF 70-200 2.8, IS L, EF 100-400 IS L, EF 300 F2.8L, and about 1 even ton of old manual focus, some of which have been modified to fit Canon. Also a Sigma EF 12-24mm
This is reduced in size, click the lick to see the big one. Taken at the local beach with a VERY beat up 300 f2.8 Body was 7D which I bought used, my first one
https://live.staticflickr.com/6133/6043395212_a7591ee54f_k.jpg
One of my lens projects. Center one is Tamron Adaptall II 500mm, other two are different versions of Sigma 600mm, both had Minolta mounts. I converted one to Canon EF, the other to M42, which then fits Canon with an additional adapter
Taken a long time ago with my Xt, an adapter, and some file work. This was a Sears/ Mamiya 50mm 1.8 in m42. But the lens had a proprietary skirt that fit down over the Mamiya mount, and I had to laborously and carefully file that away to fit an M42 to EF adapter. Click the link for full size
https://live.staticflickr.com/2415/2269089278_5ad34964f9_h.jpg
A very very lucky shot. Taken long ago with my Xt, and a modified "junk" Canon FD mount 200mm F2.8. it was pretty hacked up, and the aperture setting "is a guess."
https://live.staticflickr.com/2282/2270212441_ea210f2f9e_k.jpg