On Sep 27, 2024, at 08:32, Eli Zaretskii <eliz@gnu.org> wrote:

I have currently (length (font-family-list)) = 582 font families
installed. And whenever I input some ununsual characters, Emacs will
freeze for seconds until I am able to do anything else.  Worse, the
freeze delay for each character will add up.  And whenver the face
changes (including hl-line-mode), or I switched to another buffer for
some time, there will be a delay again.

This part, about _any_ unusual characters causing a significant delay,
seems to imply that the default fontset is not set up correctly on
your system (or maybe in general on macOS), or perhaps that the way
the fontsets are used on macOS is very different from other systems.
For starters, are the fonts that Emacs selects for the characters you
used for testing different from the fonts defined by fontset-default
for those characters?  If so, what happens if you modify
fontset-default (using set-fontset-font) to specify for these
characters the same fonts as what Emacs selects with the default value
of fontset-default? does font selection become much faster (it
should)?

If specifying the precise font in the fontset doesn't speed up font
selection, then something is very wrong with how fontsets are used on
macOS.  Emacs comes with the default value of fontset-default that is
already configured for many characters, and the ones you show should
be included.  So I'm puzzled why you experience such long delays when
some of those characters are used.

It could also be the matter of selecting the default face's font.  For
best results, it should be a font that covers many popular scripts, at
the very least Latin, Cyrillic, and Greek.  Judging by the "unusual"
characters you show, it sounds like Latin characters are not well
covered by your default face's font?  If so, perhaps choosing a font
with better coverage will make the situation better for you?