Setting `set macthinstrokes` doesn't have any effect

It looks like there has been regression and the set macthinstrokes option stopped working at some point

Describe the bug
set macthinstrokes doesn't change the way the font is rendered

To Reproduce

1. Run gvim --clean
2. Set the thin strokes option with :set macthinstrokes
3. Observe nothing happens, the font is exactly the same as it was before running the command

Expected behaviour
The font should be slightly thinner

Screenshots
With set macthinstrokes

Without set nomacthinstrokes

Environment:

VIM - Vi IMproved 8.2 (2019 Dec 12, compiled Apr  1 2021 08:37:51)
macOS version - x86_64
Included patches: 1-2681
Compiled by GitHub Actions
Huge version with MacVim GUI.  Features included (+) or not (-):
+acl               +file_in_path      -mouse_sysmouse    -tag_old_static
+arabic            +find_in_path      +mouse_urxvt       -tag_any_white
+autocmd           +float             +mouse_xterm       -tcl
+autochdir         +folding           +multi_byte        +termguicolors
-autoservername    -footer            +multi_lang        +terminal
+balloon_eval      +fork()            -mzscheme          +terminfo
+balloon_eval_term +fullscreen        +netbeans_intg     +termresponse
+browse            +gettext           +num64             +textobjects
++builtin_terms    -hangul_input      +odbeditor         +textprop
+byte_offset       +iconv             +packages          +timers
+channel           +insert_expand     +path_extra        +title
+cindent           +ipv6              +perl/dyn          +toolbar
+clientserver      +job               +persistent_undo   +transparency
+clipboard         +jumplist          +popupwin          +user_commands
+cmdline_compl     +keymap            +postscript        +vartabs
+cmdline_hist      +lambda            +printer           +vertsplit
+cmdline_info      +langmap           +profile           +virtualedit
+comments          +libcall           +python/dyn        +visual
+conceal           +linebreak         +python3/dyn       +visualextra
+cryptv            +lispindent        +quickfix          +viminfo
+cscope            +listcmds          +reltime           +vreplace
+cursorbind        +localmap          +rightleft         +wildignore
+cursorshape       +lua/dyn           +ruby/dyn          +wildmenu
+dialog_con_gui    +menu              +scrollbind        +windows
+diff              +mksession         +signs             +writebackup
+digraphs          +modify_fname      +smartindent       -X11
+dnd               +mouse             -sound             -xfontset
-ebcdic            +mouseshape        +spell             +xim
+emacs_tags        +mouse_dec         +startuptime       -xpm
+eval              -mouse_gpm         +statusline        -xsmp
+ex_extra          -mouse_jsbterm     -sun_workshop      -xterm_clipboard
+extra_search      +mouse_netterm     +syntax            -xterm_save
-farsi             +mouse_sgr         +tag_binary
   system vimrc file: "$VIM/vimrc"
     user vimrc file: "$HOME/.vimrc"
 2nd user vimrc file: "~/.vim/vimrc"
      user exrc file: "$HOME/.exrc"
  system gvimrc file: "$VIM/gvimrc"
    user gvimrc file: "$HOME/.gvimrc"
2nd user gvimrc file: "~/.vim/gvimrc"
       defaults file: "$VIMRUNTIME/defaults.vim"
    system menu file: "$VIMRUNTIME/menu.vim"
  fall-back for $VIM: "/Applications/MacVim.app/Contents/Resources/vim"
Compilation: clang -c -I. -Iproto -DHAVE_CONFIG_H -DFEAT_GUI_MACVIM -Wall -Wno-unknown-pragmas -pipe -DMACOS_X -DMACOS_X_DARWIN -g -O2 -arch x86_64 -arch arm64 -U_FORTIFY_SOURCE -D_FORTIFY_SOURCE=1 -Wall -Wextra -Wshadow -Werror -Wno-error=missing-field-initializers -Wno-error=deprecated-declarations -Wno-error=unused-function
Linking: clang -L. -fstack-protector-strong -L/usr/local/lib -L/usr/local/opt/libyaml/lib -L/usr/local/opt/openssl@1.1/lib -L/usr/local/opt/readline/lib -L. -fstack-protector-strong -L/usr/local/lib -L/usr/local/opt/libyaml/lib -L/usr/local/opt/openssl@1.1/lib -L/usr/local/opt/readline/lib -arch x86_64 -arch arm64 -L/usr/local/lib -o Vim -lm -lncurses -liconv /usr/local/lib/libintl.a -framework AppKit -fstack-protector -L/System/Library/Perl/5.18/darwin-thread-multi-2level/CORE

Additional context

MacVim uses exactly the same API as iTerm2

MacVim:
https://github.com/macvim-dev/macvim/blob/ef048edbb7aa6a65d11c7345ea7ca71d9748462a/src/MacVim/MMCoreTextView.m#L755-L758

iTerm2:
https://github.com/gnachman/iTerm2/blob/c52136b7c0bae545436be8d1441449f19e21faa1/sources/iTermGraphicsUtilities.m#L43-L51

In iTerm2 it is working great, so apparently, there is something wrong and that code in MacVim is never reached

Here are the iTerm2 screenshots:

with the thin strokes option

without the thin strokes option

Beginne bei den verlinkten Zeilen um 755–758 in MacVim/MMCoreTextView.m und vergleiche dessen Core-Text-Verarbeitung mit dem Code in der verlinkten iTermGraphicsUtilities.m. Reproduziere das Verhalten mit gvim --clean und :set macthinstrokes und bestätige anschließend, dass die Einstellung für dünne Striche die gerenderte Schrift erwartungsgemäß ändert.