for posterity (because I had to figure out how to figure out the app_id): I wanted to have cathode pop up in a sticky floating window in sway just like mpv does (so I can watch stuff in a nice floating window that sticks between workspaces like I have MPV doing)

So that's (in ~/.config/sway/swayconfig or your swayconfig):

for_window [app_id="io.github.andunieee.Cathode"] floating enable for_window [app_id="io.github.andunieee.Cathode"] sticky enable