So I set the theme to Papirus, which came pre-installed. Most icons are ok I think, but I am still missing icons in tint2 for Slack, Freetube, and Firetools. I get a generic window icon.
The kitty terminal icon in the tint2 panel is also different from the Papirus theme icon.
Tried uninstalling the icon theme and reinstalling following the instruction on github (installed to root), but no dice.