I have GNOME set up with a custom icon theme and Dash to Dock. Most programs work exactly as I want them to, but OpenShot and Zoom don't want to play by the rules:

As you can see, OpenShot and Zoom, when opened, use their default icons which clash badly with my icon theme, and they get added to the end of the taskbar instead of grouping with their icon in the favorites section. I made sure their .desktop entries are referencing the right icons and I tried reinstalling both of them after setting the icon theme; both solutions did not help. This is on Gentoo, if that matters, and I set the icon theme using GNOME Tweaks. Any ideas?

I figured out the issue after some digging. Apparently certain programs treat the desktop launcher as a wrapper and the created window has a different class from the one the launcher causes GNOME's dash to expect. I moved /usr/share/applications/org.openshot.OpenShot.desktop and /usr/share/applications/zoom-zoom.desktop to openshot.desktop and zoom.desktop respectively and added the line StartupWMClass=openshot/zoom to the respective entry and that fixed it. I imagine this solution will apply for any similar grouping issue with the GNOME dash.

Edit to add a small clarification: I don't think moving the launcher locations was actually the meaningful part of the solution. I had to symlink a new zoom-zoom.desktop back to zoom.desktop because it doesn't like it being located at the new filename when launching a meeting from the web browser, but using zoom-zoom.desktop as the launcher still worked, so I think you only actually need to change the StartupWMClass line and there's no need to move the .desktop entries.