It is a limitation of a PWA. A native app (wrapper) will likely be coming though, and a custom Capacitor plugin could theoretically interface with the native API to switch out icons. Theoretically. No promises though :)
Quoting this comment by the dev
I like that you can develop for both iOS and Android at the same time. And no need to verify every update towards the store.
Agree. This is a ridiculously good implementation and I don’t understand why nobody has gotten this right until now. Hallelujah holy shit.
Voyager has converted me into a PWA believer.