2020 iMac won't let second monitor sleep

[ScreenSavers]

My 2020 27" iMac with the max GPU won't let my external 31.5" 4K monitor sleep- it's connected via USB C and works just fine, but when the iMac is asleep, the monitor flashes in and out of sleep mode and says "no signal" on the screen every couple minutes. With other computers, I have no issues, and the monitor stays in standby just fine. I had the issue on Catalina, and reinstalled macOS and am now using the latest beta of Big Sur now. Any ideas? It's really frustrating and annoying, and I've been turning off the monitor but it takes forever to turn back on and get ready, and it rearranges my desktop icons and dock position...

 

[ScreenSavers]

I guess nobody else has experienced this?

 

[jezzastern]

I had a similar problem recently when connecting a 2018 21 inch iMac to an external display. I solved the problem by changing from a generic cable to a reputable one, connecting via USB-c to DisplayPort.