I'm using Emacs 29.2 on OSX and I'm having difficulty selecting a 
font with the proper weight. The following simple script shows the 
problem on my machine:

(set-frame-font "Roboto Mono-14:light")
(insert "test")
(insert (propertize "test" 'face '(:family "Roboto Mono" :weight 
light)))

The set-frame-font installs the proper font and weight.
The first insert displays the text with light weight (as expected)
The second insert displays the text with a *regular* weight 
(unexpected).

When I ask for char description for both displayed strings, Emacs 
reports " mac-ct:-*-Roboto 
Mono-regular-normal-normal-*-14-*-*-*-m-0-iso10646-1" for both 
strings (even though the visual appearance is clearly different).

I think the problem has been here since at least version 28.0 (and 
I solved it by creating a dedicated font file with a new name).

All necessary fonts are installed:

$ fc-list "Roboto Mono" -f '%{weight} %{style}\n' | sort -n

0 Thin
0 Thin Italic
[0 200]
[0 200]
50 Light
50 Light Italic
80 Italic
80 Regular
100 Medium
100 Medium Italic
200 Bold
200 Bold Italic

Nicolas