Have Catalina, Big Sur, Monterey and Ventura on my Mac Pro 3,1 each on their own drive and I can boot any one of them, Works perfect, Use the Nvidia EVGA GTX 780Ti and sometimes the Nvidia EVGA GT 730, They seem to work with everything all the time, EVGA still sells the GT 730 on their website new, Could probably get a lot of other cards to work but these two I like because they are easy
Did the same thing with the Mac Pro 5,1, Works perfect
Have a Mac mini 2014 with Monterey and Sonoma each in their own drive, Works perfect
Have a Mac Pro 6,1, Put Monterey on it which it is suppose to have and partitioned the 1TB SSD to 2 500GB and put Sonoma on the other, and it works perfect with everything just like it is suppose to
Somebody want a real Mac to use that works just like it suppose to for the average person that don't do the big fancy stuff all these work just fine, Will probably to some of the big fancy stuff also, I know all of them will defiantly do cad, Even put parallels on one Mac Pro 5,1 and run Windows 10, Windows 11, and Linux, even have windows 7 32bit on the Mac Pro 5,1 to run a 32 bit Cad app I like to use, With 64GB Ram I can run MacOS plus 2-3 other operation systems all at the same time
An absolute fact, Done it