Cannot run project on Steam Deck, cannot install missing binaries (?)

I’ve configured my Steam Deck and wanted to run my game on it.
This pops up when I switch the platform to Steam Deck.

Weird, because Steam Deck runs regular Windows binaries, but I select to download.

Then this window pops up:

Does this want to download whole new copy of UE? I cannot select the directory my UE installation is already in, so I select a different path:

But after confirming, I’m stuck on “Queued”, it never progresses past that.