Steam and Battle.net are so annoying here. Three years on and what are essentially web browsers still haven't be compiled for Apple Silicon. Bnet keeps getting worse and I don't even run Steam anymore, there's no point.

It boots fast on Windows and Linux so probably?

Or Valve cares about it as much as about Counter-Strike on Mac? There is no technical reason for it to be that slow.

Does that run on ARM instruction directly or through the x86 emulation layer?

The latter

Just tried this, 8 seconds with my 2020 MBP (2 GHz Quad-Core Intel Core i5, 16 GB 3733 MHz LPDDR4X)

yes