Musescore 4 Bug - Guitar Harmonics

Proper playback of those would probably require a Muse Sounds for guitar, which is not available yet.

I too battled with harmonics when I started using MuseScore 4, but then discovered this method while working on something else... so if it is a bug, here is a workaround - which could be put in the manual as a method for harmonic entry.
1. Enter the note you want to be played (i.e., as it should sound).
2. Change the note head to diamond (or other shape if you want to)
3. Add stave text "arm.12' or "harm.12" or whatever you want to show.
Now the important bit:
4. With the note selected, right-click and pick 'Edit element' (or press F2 or Alt+shift+E). Use the down arrow key to move the note down to where you want it to be shown. It will still play the note as originally entered in step 1.
Peter.

Another workaround I have been using with for harmonic in Musescore 4 s is the Mid-score instrument change. (this will only work in Musescore 4 though a similar strategy can be used in other versions of Musescore):
1. First set up your score with the guitar sound you want to use. Classical is what I am using.
2. Select the note you want the harmonics to start on and from the “Text Pallet” (not from the “Add” -“Text” menu up top which will not work) and select “Change Instr.”
3. Select another guitar other than Classical, in my case Acoustical. Please note if you are using tablature you must use a similarly strung guitar: Acoustical, Electrical etc.; otherwise Musescore 4 will blow up in a catastrophic crash. In other words, do not select a piano, violin, etc.
4. In the mixer, change the Acoustical guitar to the sound you want I use the Muse Harp under Muse Sounds but there are many other sound fonts available including a free VST3 Guitar Harmonic sound font that you can download.
See uploaded sample. Note that I started with the harmonic guitar “Harm” i.e. Acoustical and changed to Classical “Guit” (note the parentheses around Classical in the mixer)