I suspect that Apple's DisplayPort drivers are partly at fault here. Way back in 2015 or thereabouts, my office MacPro had serious trouble talking to my Philips 40" 4K monitor. I'd have to power cycle the monitor after every time the computer went to sleep. Then, after some macOS upgrade or other, that problem went away. Now returning from sleep is wonky (the monitor blinks in and out for a few seconds), but at least stable.

For contrast, my home MacPro is connected to a Panasonic Sharp 32" 4K monitor that was, at that time, sold directly by Apple. That's always been stable. Given this, I also suspect that early DisplayPort monitors have varying degrees of standards compliance in their implementations.

In wildly unrelated news, my father -- a computer engineer -- is getting himself an M1 MacBook something or other as an upgrade from an earlier machine that predates Apple's adoption of USB-C / Thunderbolt. This means that I've been trying to explain the world of USB-C, alt modes, Thunderbolt, and so forth. It's baffling just how complicated it's become.