To be honest, Canon EF mount lenses are probably the best buy if you are looking for compatibility: there's adapters for Sony E-Mount, Canon RF-mount, etc.
The reason RF, Z, and E mount exist is because you can make the camera body much slimmer in MILC.
It's much easier building adapters for lenses going from DSLR -> MILC. It might not be possible to go the other way around.
As a result, there is a wide range of third party lenses evailable for Sony FE, none for Canon RF.
I real shame as I would love to use some of Sigma glass on there without use of the EF adapter.
One of the problems Canon has faced recently is a flooding of the market with super cheap lenses (we're talking 50-200 dollars for total junk). The people that are buying them are justifiably upset when the photos are crap because they incorrectly think its a camera problem. Hey, a lens is a lens, right?
Anyhow, there's wide speculation that Canon will license to the quality quality third-party makers at some point [1][2].
[0] https://petapixel.com/2022/09/06/canon-confirms-its-going-af... [1] https://www.canonrumors.com/forum/threads/sigma-to-make-a-ma... [2] https://www.canonrumors.com/forum/threads/the-state-of-third...
https://fstoppers.com/gear/canon-breaks-silence-viltrox-lens...
Vintage glass is great, if you get it good condition.
I own a perfectly functioning 40D from 2007 myself, which I replaced by a Sony A7III just recently, as I hate the fact, that Canon tries to force their customers to buy their own expensive RF lenses.
Of course cameras are impressive pieces of technology. Still I understand the sentiment of the above commenter. My last comment was an overstatement, still there is a substantial chance of a hardware failure.