The SIGGRAPH Latex style changed to the Libertine font. Here're the steps to convince Latexit to use the new stylesheet and then to convince Illustrator to use the libertine font for drag and drop math.
mkdir ~/Library/texmf/tex/latex/local/acmart.cls/
cp ~/Dropbox/boundary/Paper/acmart.cls ~/Library/texmf/tex/latex/local/acmart.cls
In Latexit, open up Preferences, add a new SIGGRAPH "Template" containing:
\documentclass[sigconf, review]{acmart}
\pagenumbering{gobble}
If you try to drag and drop these into illustrator you'll see that illustrator has replaced the nice math font with Myriad or something silly.
Download the TTF libertine font pack
Drag this into FontBook.app
cp /usr/local/texlive/2020/texmf-dist/fonts/type1/public/libertine/*.pfb ~/Library/Application\ Support/Adobe/Fonts/
Update: I also had to issue:
cp /usr/local/texlive/2020/texmf-dist/fonts/type1/public/txfonts/*.pfb ~/Library/Application\ Support/Adobe/Fonts/
cp /usr/local/texlive/2020/texmf-dist/fonts/type1/public//newtx/*.pfb ~/Library/Application\ Support/Adobe/Fonts/
If you see boxes with X's replacing symbols after dragging and dropping from LaTeXit, then drag into Finder instead (to create a .pdf file), then open this directly and Illustrator will give a warning and tell you which font it's (still) missing.
Restart Adobe Illustrator
Update:
I also added:
cp /usr/local/texlive/2020/texmf-dist/fonts/type1/public/amsfonts/cm/*.pfb ~/Library/Application\ Support/Adobe/Fonts/