On Macs with the M1 chip, there is a bug with ultra-wide and “super-ultra-wide” displays. The problem lies in the definition. Some definitions are supported by the external display but are not available.
Apple is aware and has confirmed that a fix will be introduced in a future macOS update. The manufacturer states on its website:
When you use the Apple M1 chip to connect an ultra-wide or super-ultra-wide display to your Mac, some resolutions that your display supports may not be available.
Apple is aware of this issue and the resolution is planned for a future macOS update.
No information is currently available on the date of the patch. Apple also does not say whether the update will be carried out with an update such as macOS 11.2. Or whether it is a separate update.
Under System Settings> Monitor you can select “Default Screen Setting” or “Scaling”. If you hold down the Option key while you click Scale, you can choose an exact definition for the screen. This point is currently problematic with the Mac M1.