not quite sure what you mean here.. I only bought the R5 body because the EF lenses I had (investment) would work. I even tested ahead that my key Sigma EF lenses (20mm and 35 mm ART primes and 150-600C) would work on this (and some native canon lenses like 180L macro).. or it'd have been a no go. Canon has had a large array of 3rd party lenses, and they do work via EF adapter, so while it was wrong, it is a fairly natural assumption that they'd likely continue.. didn't quite expect them to be as tight on control beyond first year or two, especially how wishy washy their answers were and still are.
Is it end of world? Will I stop using Canon right away? No, but it certainly doesn't endear a long time customer of theirs to them (D60 (not 60D, but the 6 megapixel original SLR), 40D, 7D, 80D, R5.. many G series etc) and a bunch of lenses with this behaviour. I do have 1 RF lens (24-70 2.8L), but unsure if I'll continue investing further unless I see a change. Not a threat or whine, but just a reality that I don't wish to further continue if options don't appear (but will enjoy what I have). The main reason I went Canon for so long was precisely because they seemed open to 3rd party lenses and even firmware (magic lantern was a huge motivation).
Adapter works fine, native mount is easier to deal with than constantly changing out adapters.
I get it is a business decision, and I get I'm not likely their main base... but I am part of a fair # of users... and frankly except for edge cases (action, macro, wildlife etc), most of the camera industry is disappearing to phones... alienating some of their longer term customers to protect some segments that may disappear anyway seems counter-intuitive... but as a member indicates, it's a business, they have the figures and they make the choices.. just like we do whether to spend there or not. The R5 + the RF 24-70L 2.8 was about $10k CAD at time.. not a small amount to sneeze at.