Check out my hobby project https://dosdeck.com
It allows you to play games like Commander Keen, One Must Fall 2097, Warcraft, Jazz Jackrabbit, Command & Conquer, DOOM, Heretic and many more to come. All configured to play on the Steam Deck using the controller. All games are carefully selected to be either freeware, shareware, demos or full versions.
It takes some fiddling to set up properly on the Steam Deck, but I’ve put the details on the About page.
Hope you like it! ^_^
Find me on /r/dosdeck
Man, this reminds me of the old days when we would put flash files onto the PSP, and aim the browser at the local file to play them.