Given their rivalry with Valve (I’m sure Riot see it as a rivalry at least, Valve probably don’t) I wouldn’t put it past Riot to want to avoid SteamOS and Linux by extension until significant market share is available.

To be 100% honest, probably not, and you may need to confirm with someone who knows Valorant. The big issue is anti-cheat, the detectors in use for major multiplayer games tend to lose their minds when they see Linux as they’re typically only built for Windows. Other than anti-cheat, it wouldn’t surprise me if it played better on Linux. Some of the low level magic has improved a lot in recent years, but official support is mandatory for multiplayer.