Tamil text is not shaped properly in the modeline.  Please view the
attached file "Noto_Serif_modeline.jpg" to see what I mean.  I set
"tamil" script to use "Noto Serif Tamil" in the default fontset like so,

    (set-fontset-font "fontset-default" 'tamil '("Noto Serif Tamil" . "iso10646-1"))

Changing the font to "Lohit Tamil" [1] does not fix the shaping issue so
Noto Serif Tamil is not the problem (See file
"Lohit_Tamil_modeline.png").

As shown in "Noto_Serif_Expected.png", the text is shaped as I would
expect, in the minibuffer.

To see if this was specific to Tamil, I tried creating a buffer named
"मेरा" and "नमस्कार" ("mera" and "namaskaar C-b DEL" in devanagari-itrans)
but they are shaped better (but not the same as in-buffer text).  I also
set "devanagari" script to use "Noto Serif Devanagari" in the default
fontset.

I also see the problem in a GTK3 build of Emacs 27.2 (sorry, I do not
have the time to check Emacs 28 or Emacs 29 GTK3, PGTK build right now).

1. https://releases.pagure.org/lohit/lohit-tamil-ttf-2.91.3.tar.gz