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I'm using the built-in Screen Sharing client in macOS to connect to a Mac Mini 2020 M1 by running Connect to Server in Finder and choosing the vnc://machine-name.local link.

The connection works fine, except for one thing: It keeps changing resolution approximately every 10 seconds. The effect is that what is shown in the client window changes between the whole screen and a fraction of the screen.

If I open the Displays setting through VNC it just shows the ordinary settings for the ordinary display. I can set it to Scaled and specify a certain resolution, but that does not help.

The Screen Sharing Preferences has a few options that seem related to the display, e.g. Show full size and Show the screen at full quality. I have changed them in all combinations that I can think of. Nothing has made any difference.

There is also the Scaling toggle in the toolbar of the Screen Sharing app. Again, it doesn't seem to do anything (what is it supposed to do?).

I have also tested connecting with the RealVNC vnc-viewer, it had the same issue.

The Mac mini is not really headless, it does have a monitor connected to HDMI, but the monitor is mostly turned off.

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  • I just earned the necessary reputation to post everywhere so I'm copying this comment here: "Show the screen at full quality" is for screens of computers you’ve never connected to before, so take View > Full Quality
    – Elio Labbia
    Commented May 31, 2022 at 17:18
  • "flashing between Retina and not, i.e. it toggles between fuzzy and sharp". This could also be related to Wi-Fi bandwidth fluctuation. Check your signal with some good tool like WiFi Signal
    – Elio Labbia
    Commented May 31, 2022 at 17:51

2 Answers 2

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I lack the necessary reputation to add a comment, so please bare with me if I add it here.

I believe that setting a specific display resolution beforehand (e.g. 2560 x 1440) is important for its stability during the connection.

When you clicked Scaled did you get additional resolutions by pressing and holding down the Option key or was it one of the four recommended resolutions, scaling from Larger Text to More Space?

Otherwise, I'd recommend installing Display Menu or EasyRes (both Free on Mac App Store) to set that resolution.

If none of these work, other Screen Sharing protocols such as Apple Remote Desktop (pretty expensive) or the two solutions from Astropad (Luna Display and Astropad itself in Mac-to-Mac Mode) might work better.

More often than not your Mac Mini will be running Headless or the plugged screen will be turned off. An inexpensive solution would be an HDMI Dummy Plug (an adapter designed to plug into the HDMI port of your Mac). Newertech, for example, has one of these at a very affordable price (they had one at under $15, but I can't seem to find the link right now). This will allow you to have a display emulator with a reliable preset resolution.

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  • Yes, I've tested the additional resolutions you get by Option-clicking
    – Klas Mellbourn
    Commented May 31, 2022 at 15:02
  • How would I set "a specific display resolution beforehand"? I can't find such an preference in Screen Sharing
    – Klas Mellbourn
    Commented May 31, 2022 at 15:03
  • May I ask which resolution you selected through Option-clicking and is it sticking during the session?
    – Elio Labbia
    Commented May 31, 2022 at 15:29
  • Also, is your Mac Mini running Headless?
    – Elio Labbia
    Commented May 31, 2022 at 15:41
  • I just added a new section about HDMI Dummy Plug adapters to have a display emulator with a reliable preset resolution.
    – Elio Labbia
    Commented May 31, 2022 at 15:59
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You have several options:

Check the display settings on the Mac Mini

  • Open System Preferences and:
  • Change the display resolution to "Standard"
  • Switch any enhancement like True Tone etc off.
  • Check the color profile and change it to default if necessary.

Check Energy Saver on the Mini

  • Go to System Preferences and head to Energy Saver
  • Search for Automatic Graphics Switching option and untick it. (That option is not available on Mac Airs)

Restart the Mini in safe mode

  • Restart your Mac by pressing and holding the power button and shift the key

Reset NVRAM (or PRAM)

  • Restart your Mac by pressing and holding Option+Command+O+R simultaneously for a few seconds

New User

  • Create a new user on the Mac Mini (no kidding)
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  • I can't find any preference named Automatic Graphics Switching (or even Graphics). This is a Mac mini, always connected to power.
    – Klas Mellbourn
    Commented Jun 1, 2022 at 17:55
  • I don't have any enhancements in Display (My monitor is connected through a sony receiver to a 1920x1080 projector). I tested changing the color profile. Did not help.
    – Klas Mellbourn
    Commented Jun 1, 2022 at 17:57
  • @KlasMellbourn What about the other solutions?
    – Rafo
    Commented Jun 4, 2022 at 13:33

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