Strange operation of keyboard shortcut on my iMac. Any ideas on what I'm seeing?

OPS – should have said ⌘F5 and ⌘F6 instead of ⌘5 and ⌘6 in this post. Corrected below:

I happened on a setting I hadn’t noticed that allows ⌘F5 and ⌘F6 to adjust screen brightness on my iMac from my ancient, non-Apple keyboard:

Well, it doesn’t work, but that isn’t my issue! What it does do, for ⌘F5, is:


All the windows are gathered to my external monitor and then mirrored to my iMac display! There doesn’t seem to be any function, other than this weird shortcut, that accomplishes this. If I disable the shortcut, ⌘F5 does nothing. If I change the shortcut to something else, ⇧⌘F5, that key combo does nothing!

I’ll probably report this to Apple, when I get the beta for 10.16, assuming it does the same. Certainly too late for a fix to Catalina!

I think you missed an F there, as it’s ⌘-F5 and ⌘-F6.

Not sure why ⌘-5 works that way on yours, doesn’t do that on my standard Catalina.

Mirroring the display does that.
If you change “Optimize for”, it will switch the other way (ie. my imac screen would by vertical on my external).
(I set my external to rotated 90° to illustrate.)


Yes, corrected ⌘5 to ⌘F5, which I meant to say. OK, so it is mirroring and optimizing for the external. There doesn’t seem to be a keyboard shortcut possible to do that, except for ⌘F5 on my system that is supposed to be lowing the brightness. Hmm.

This might help figure out who (which program) is doing this.

Yes it shows it is loginwindow. Seems to me this is beyond the scope of what loginwindow is supposed to do.

Looks like it is normally ⌘-F1.

I noticed that on an Apple keyboard Fn-F1 turns brightness down, which is what ⌘-F5 should be doing on my iMac with an non-Apple keyboard. While I can verify that ⌘F1 should mirror switch (and doesn’t do so on my keyboard) it also appears to be hardwired in (unchangable by any method) according to what I read. I suppose I should dig out and connect an Apple keyboard to see what happens. I’ll try that tomorrow. No time to deal with that today.

I’m using a non-Apple keyboard (Matias Ergo Pro) with my iMac Pro, and Fn-F1 and Fn-F2 control brightness.

My non-Apple keyboard doesn’t even try to be. There is no Fn key. If I plug in an Apple keyboard the section of Display Shortcuts (shown in my first post) disappears. And ⌘F5 no longer toggles mirroring.

I suspect this is an edge case that wasn’t properly beta tested. (Call me guilty as a beta tester, this was probably bad for many versions yet I didn’t see it until now. But I will report it to Apple.)

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