Can't pin Desktop icon to dock favorites in Pop!_OS

I'm using Pop!_OS 22.04. I just downloaded and installed a new app (PyCharm), but it didn't come with an icon for my dock. I created a new icon using this ~/.local/share/applications/pycharm.desktop file:

[Desktop Entry]
Encoding=UTF-8
Version=1.0
Type=Application
Terminal=false
Exec=/opt/pycharm-2022.1.1/bin/pycharm.sh
Name=PyCharm
Icon=/home/USERNAME/Pictures/icons/pycharm.png

This seems to work great. I can see the icon I chose when I look for the app, and it opens in my dock. The only problem is that I can't seem to pin it to my dock's favorites. The "Add to Favorites" button that every other dock icon has when I right click on them doesn't appear in my new icon at all. Am I doing something wrong? Am I missing something? Is this a bug? Update: I've seen this on other apps too, but for PyCharm, turns out there's an option in the GUI to create the desktop launcher. It appears to do exactly the same thing I did (place a .desktop file in the same folder), but it also adds a few extra keys. The biggest one seems to be StartupWMClass. If that key is included, the "Add to Favorites" option appears when you right-click the icon in the dock. If the StartupWMClass key is not present, the "Add to Favorites" option is not there. Why is that? What does that option do?