Hello,
Since Emacs 28 I have a new problem with Arabic fonts.
1. I can't change the Arabic characters to the font of DejaVu Sans
Mono (or others). This wasn't a problem before.
2. The old one: As you can see the glyphs aren't correct, the '-'
after س is not correctly placed. It's in the place of the glyph of
س. Sometimes I have the opposite problem: gaps between the
characters. It depends usually of 'text-scale-adjust', if I change
the scale the problem can disappear.

(Of course I started Emacs with the '-Q' option.)
Attachment: To see the difference: a screenshot in Word/LibreOffice Writer:
In LibreOffice:
1. The font is correct (also for the Arabic characters)
2. The '-' is at the correct place
Can Harfbuzz be a problem? In the older emacs version (maybe 3 or 4 years 
ago?) I never had these problems.

Kind regards
Frank