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When attaching a very small (720x480) external display (SmartBeam portable projector) the main laptop display switches to mirroring the smaller display (at an unusable resolution and scale) rather than using it as a secondary monitor.

Below are screenshots of System Information and the desktop.

The Displays menu in System Preferences only shows the main laptop display, but with no options for changing resolution (even when "Show all resolutions" is enabled in the Advanced menu).

Why is this happening and is there a fix?

screenshot of the System Information, Graphics/Displays section screenshot of the macOS desktop, at a very very low resolution

Ferdia McKeogh
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  • @Allan It will not go into any mode that is not mirroring. I have clarified the title. – Ferdia McKeogh May 21 '23 at 13:09
  • Have you checked the display settings in System Preferences? – Solar Mike May 21 '23 at 13:12
  • @SolarMike I have, it only shows my laptop display and no others, but the resolution slider disappears when the external display is connected. I have edited the question to reflect this. – Ferdia McKeogh May 21 '23 at 13:14
  • Did you review this document? https://support.apple.com/guide/mac-help/extend-mirror-mac-desktop-multiple-displays-mchlb5f905a1/mac – Allan May 21 '23 at 13:14
  • @Allan I did, but since the external display does not appear in System Preferences, and no mirroring options appear in the menu bar, I cannot change the settings described in that document. – Ferdia McKeogh May 21 '23 at 13:16
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    There was a similar question (no answers) posted about a month ago. My contention is that the massive disparity in resolutions is a problem and macOS resorts to the “least common denominator.” Unfortunately, I don’t have any lower rez displays anymore to test with to validate this theory. – Allan May 21 '23 at 14:05
  • @Allan That makes sense, thank you! – Ferdia McKeogh May 21 '23 at 18:59

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