6.7 isn't supported on any platforms that don't have it listed on the support page. I pulled up the link to the 6.7 image, but there aren't any 12th generation PowerEdge servers shown supported. 

I think a friend of mine has ESXi 6.7 running on a pair of R720s in his home lab, but I'm not sure how much work it was to set up. I'll try to follow up and see if it worked out.

I talked to my friend. He is running 6.7 on a pair of R720s. It's not supported, by Dell, though.

I wouldn't expect it to work by default. I looked at the list of compatible systems and they were all 13th and 14th generation systems. That's not to say you *CAN'T* do it successfully, but I expect it'll take a bit of effort to make sure any and all missing drivers get added. I haven't done anything with that release of ESXi, so that's about all I can think to suggest, if you want to try it.

i assume then that upgrading to esx 7.0 is a very risky proposition...

As the others already told.... on paper not supported by the HCL...but other than that 6.7 runs very well on every 12Gen Dell PowerEdge (We have 3 dozen of them and all runs 6.7u3).

About 7.0.  VMware drops support for drivers based on vmklinux API and only "native" drivers can be used. That kills a lot of the older metal.

Regards,
Joerg