Not sure how powerful this "potato PC" is, but if it is powerful enough for GBC emulation, I'd suggest
Augury Red Code. Available
on Itchio, it's a homebrew focused on platforming and, if you're interested, speedrunning.
Wishing Sarah (Game Boy homebrew) should be playable if this potato PC can also handle this sort of emulation. Available for free only
on Itchio, it's a puzzle game with horror elements, and it's an interlude between Dreaming Sarah (paid game, Windows) and the upcoming Awakening Sarah.
And if this PC can handle NES emulation, I'd highly recommend the platformers
Böbl (
Itchio page) and
Yun (
devs' page).
Phoenotopia (Adobe Flash version) should be pretty light too. It can be found on Bluemaxima's Flashpoint, but it doesn't require the launcher to run, only a working executable of the portable Flash Player (even the one Flashpoint uses should be perfectly functional). The game itself is a sidescroller action RPG, and my first impression when playing that game was "am I really playing a Flash game?". It felt far better than quite a few recent indies I had played.