In practice it mostly affect studio making over 1M in sales per year. The download fee only occur on pro users past that threshold. The fee is so ridiculous that they’re basically forcing devs to get pro, but that was kinda already a thing anyway. For studios malong over 1M a year, well they gotta pay up unfortunately. Unfortunately 1M per year ins’t that much for a middle-sized studio, but small studio are barely affected by this change.
I made games primarily for Windows which we also compiled for Linux. It is mostly input/output stuff, aka hardware issues. That is, audio issues, input issues, storage issues, dependency issues. Modern game engine mostly handle the rest. It wasn’t such a big deal to fix, but most gamedev lacked experience with Linux, and most projects are already over budget and late, so fixing Linux for an extra 2-5% of sales didn’t make much sense at small scale. Proton kind off fixed all of this tho.