USB C external monitors 26.6.2 problem after macOS upgrade.

Since both displays started doing this immediately after the macOS update, I’d check the display settings before changing cables or adapters.

For the Samsung, go to System Settings > Displays, select it, and set Refresh Rate to a fixed value instead of Variable/Adaptive if that option is available. Apple notes that Adaptive Sync can cause flickering or stuttering on some external displays.

I’d also test each display separately, connected directly to one of the rear Thunderbolt/USB-C ports on the Mac mini, with no hub or dock in between. Apple specifically recommends a direct connection when troubleshooting an external display.

If both displays are stable individually but start flashing again when both are connected, that would help narrow this down to a macOS/display configuration issue rather than two displays failing at the same time.

It seems to be a recurring issue for me after updating to 26.6.2 (25G83).

I have a similar issue where my displays connected by 2 hdmi cables no longer gets detected, and i can temporarily resolve it by deleting the following files:

/Library/Preferences/com.apple.windowserver.plist

And remove every file named:

/Library/Preferences/ByHost/com.apple.windowserver.*.plist

After that i restart my macbook, and it works like a charm for a few days before i have to remove the files again.

Both monitors are Samsung S24R35xFZ set to 75 Hertz refresh rate using the same brand of cables.

that S34C50 display appears to be a 3440 by 1440 display (like 4K with the bottom missing). It features 10 bits/color (implemented with FRC dithering). Refresh rates to 100 Hz

interfaces include:

• 2x HDMI 2.0, which is very troubling because that will NOT support the top display specs over one cable. (fails just short of 100 Hz at 10 bits/color)

• DisplayPort 1.2 which supports HBR2, which supports up to the top specs of the display, even when derived from USB-C