Well, this is odd...
I am running Mojave 10.14.6 on my Trashcan Mac Pro. My boot ROM version was 13x.0.0.0.0
Yesterday I installed the "Security & Safari 14.0.1 Update" and the boot rom is now at 426.0.0.0.0, which seems to be the Big Sur version.
Also, I have the two identical Dell 4K monitors on it and for the last few years the Mac won't always start or restart with both monitors being used. I need to power off/on the monitor then all is well.
Well, I think that issue is resolved. When I powered up this morning, it started with 2 functioning monitors!
Time will tell, but it would be great is this issue is resolved.
Monitor Update:
Same issue... Only one monitor powers up. The other one needs to be turned off then on for it to display the desktop.