What are some light but fun web games to play on a Chromebook? I like speedrunning but can't find many good web games to play/run

I would look at the user @dhadha profile, many, many good games here. It also depends on what genre you prefer, so that would allow for some more clarification on what games to recommend.

Thanks, I personally like platformers.

Awesome. If you want some highly competitive ones, I suggest taking a look at exit path, this is the level, red ball and run 2.

For more casual platformers, I suggest red ball 5, pico-8 games, and scratch games

By the way, a fun game is me and my launcher if you want a fast-paced platformer.

If you like fast-paced platformers, give Shelled Shinobi and Ninja Cat a try. They're both pico-8 games, which tend to be lightweight.

You can also look at games on my profile which I play or moderate; most of the are platformer web-games of varying lengths.