For various reasons, I concluded that to use Figma on Linux, a PWA through Chromium would be best for me. Since Figma is not a proper PWA (at least not recognised by Chromium as such), I need to run flatpak run org.chromium.Chromium --app=https://www.figma.com to open it in a separate window, and I need to create a desktop entry manually.
I could figure out what values to give most keys by looking at other .desktop files, and with the help of this guide.
What I could not understand are the following:
1. Where is it best to place the icon file, and what file format does it need to be?
2. How I should refer to the icon?
In other examples I see a string that doesn’t look like a file path, but rather the WMClass for other PWAs and the AppID for flatpaks and most others.
3. Where are Chromium PWAs installed to?
Contrary to this answer, there is now “Default” or any other profile directory under ~/.config/chromium/ or under /var/lib/flatpak/app/org.chromium.Chromium/