Apple has acknowledged problems experienced when using an M1 Mac with ultrawide or super-ultrawide external monitors.
M1 Macs don’t seem to recognize the native resolution of these monitors …
If the supported resolution isn’t available on an ultrawide or super-ultrawide external display connected to your Mac with Apple M1 chip
If you connect an ultrawide or super-ultrawide monitor to your Mac with Apple M1 chip, some resolutions supported by your display may not be available.
Apple is aware of this issue and resolution is planned for a future macOS update.
To see the additional resolutions for your external display, choose Apple menu > System Preferences, click Displays, then press and hold the Option key while you click Scaled.
The final line suggests, but doesn’t promise, that you might be able to enable a more appropriate resolution through the scaled options, but it’s unclear whether that might include the native resolution.
Personally, I’m a huge fan of super ultrawide monitors, ending up with the Dell UltraSharp 49-incher.
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