Every 4K external display I've connected to every M1- and M2-series Mac running macOS has a known flickering issue with Display Stream Compression that Apple knows about and has been unable or unwilling to fix.
The only reliable fixes are to either disable that DisplayPort feature if your monitor supports it, or to disable GPU Dithering using a paid third-party tool (BetterDisplay). Either that or switch to Asahi, which doesn't have that issue.
I have been experiencing this on my 2k monitors as well (Also BENQ). I tried every "fix" under the sun, eventually it stops after enough voodoo (reboots, unplugs) and cursing.
One of the many random issues on the OS with the best UX in the world (lol). Like music sometimes stopping and sometimes switching to speakers when turning off Bluetooth headphones, mouse speed going bananas randomly requiring mouse off and on, terminal app (iterm2) reliably crashing when I dare to change any keybinding, and many other things that never happened in years of working on Linux.
If you're looking for high quality text at 4K, your options are more limited than if you're looking for gaming. This is a good roundup, and the leading Dell is superb:
We use pairs of these Dells per MacBook at our offices and provide them for WR as well. There've been no issues on this Dell or prior models on M1 through M4 (M5 iPad is fine too).
As for DSC, that's been a complaint for a minute… Example HN reader theory on DSC, from Aug 2023:
The best option was the LG UltraFine 24” 4K, which sadly was discontinued years ago.
In my opinion a QHD 23.8” panel is the next best option for developers (any M-series chip handles scaling without issues); I find the common 27” and 32” at 4K a weird spot - slightly too large, slightly too low resolution – and 5k+ options are still rare.
My Dell Ultrasharp 4K also doesn't flicker and has DSC enabled according to the on screen menu. At work there are a few old Iiyama 4K screens that flicker though, but I don't know if they even understand DSC.
I've got a 4K Samsung Odyssey that I have come to hate because of it's extreme slowness and weird behaviour (I do not recommend this line), but I haven't had any problems with flickering with either M1s or M3s.
I use two 4k displays with an M1 Pro MBP. They work without any flickering. They’re using HDMI rather than DisplayPort.
I’m also, to get the two external displays without them being mirrored, using a docking station and a display driver from Silicon Motion called macOS InstantView.
This is of course not ideal if you need DP and DSC.
It works over the HDMI ports on Minis and some Pros, and this monitor is connected to the Mac via HDMI. Source: Me, my M1 Mac mini, and my Samsung Neo G8
The only reliable fixes are to either disable that DisplayPort feature if your monitor supports it, or to disable GPU Dithering using a paid third-party tool (BetterDisplay). Either that or switch to Asahi, which doesn't have that issue.
The issue is common enough that BENQ has a FAQ page about it, which includes steps like "disable dark mode" and "wait for 2 hours": https://www.benq.com/en-us/knowledge-center/knowledge/how-to...