Games and game/steam environment variables is very high software chain. Based on what your are reporting.
Ie Phoronix: Windows 11 vs. Ubuntu Linux Performance On The AMD Ryzen AI Max PRO 390 "Strix Halo"
On a geometric mean basis, Ubuntu 25.04 was around 13% faster than the OEM install of Microsoft Windows 11 Pro that shipped on the HP ZBook Ultra G1a laptop.
Or
You need to look at something low level. There is something unique wrong with laptop + kernel combination. Most search for why a game performance badly will not help you.
There has been many reported issues of unique issues for laptops that have taken a lot of work to fix like Linux 7.1-rc4 Seeing The Latest Laptop Quirks
If you are going to use Ilm I recommend using Claude Opus or equivalent. And Run in Claude Code and start with something like “I am running the following hardware:… I am seeing performance regression when running under Linux vs windows. Start with making me scripts to test and document low level performance for both windows and Linux”