Custom resolution on MacOS (for external Display)

The game runs fine on my MBA M1 by itself. But there is an issue when I try to play on external monitor.

D3 doesn’t recognize other resolutions supported by the monitor. Native top rez on MBA is 2560x1600 with 16:10 aspect ratio. While my monitor is 4k with 16:9 ratio.

Top resolution I can run is 2560x1600 with black bars. I tried it with the other monitor (1080p). It also runs with black bars.

So, my question is simple, can I change config files somewhere or add a special command to launch the game in desired resolution on desired display?

P.S. and is there somewhere a setting for UI scaling?

P.P.S. the absurdity of situation is that, when I switch to windowed mode, game renders in native resolution of the monitor. Then I can drag borders of the window and fill almost whole display so the game runs in somewhat 4K.

Can you not run in Windowed mode (Full Screen) to achieve the 4k res?

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Can you not run in Windowed mode (Full Screen) to achieve the 4k res?
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That is the problem. When in windowed mode (full screen) game renders in 2560x1600 with black bars on top and below the screen.

Did you ever find a solution? I’m in the same situation M1 Air on an external display, it caps out at the display’s native resolution (1360x768) instead of what I’m running it at (1920x1080).