Hi @srbok! While it's not official, there is a Swift package available via GURU: Swift 5.10.1 for Gentoo on GURU Installation should hopefully be very straightforward!
I'm currently actively working on packaging up Swift 6.0.1 — if you're willing to wait a few days, I'm hoping it should be available very soon. (If you expect to want Swift 6+ in general, I'd recommend waiting until it's available; compiling Swift 6 and later will require bootstrapping with an earlier version of Swift, and unfortunately, the changes incoming will require a recompilation of Swift 5.10.1 if you have it installed.)