Yeah, IBM mainframes still use VM and run CMS and other OS inside the VM. IBM was slow to the timesharing party, their plan to make "one OS" for the 360 failed utterly, and some academics got the idea for VM that became the real OS strategy for the 370 and future machines, I saw a Youtube video where people demo VM in 1975

https://www.youtube.com/watch?v=Mo2q7d5dJgg

personally I remember using it on an IBM 3090 at the New Hampshire Insurance company in the late 1980s when I was in the computer explorers.

Sometime I think about setting up a PDP-11 emulator and running RSTS/E in it for old times sake.

I also really enjoyed running OS/9 on a TRS-80 color computer, which was a really cheap machine with serious limitations (32 character display) but I had mine (I think a Coco 3 at that point) hooked up to a TRS-80 Model 100 and a DEC printing terminal so I had a Unix-like experience on three consoles, my impression was that OS/9 was a better OS than anything mainstream on IBM PC hardware at the time.