Regarding Linux: i am currently looking for an "old" laptop with a reasonable amount of cpu and graphics power and will try out Bazzite. If you are interested in the topic, i can recommend this blog: https://solar.lowtechmagazine.com/
Regarding software performance: yes, but the idea is to look at demakes and retro games, open source and ressource efficient software will also play a role in the project. I can post a link to the reports when they are ready to be published. The attached graph is in german, it shows the relation between comments on Reddit and Steam in different categories (Nachhaltigkeit = sustainability).
Regarding the steam vouchers - totally true, should have thought of that...
Kind regards,
Thomas