I am actually looking for some games i can speedrun, but i prefer if you can speedrun it in less than 40 minutes. I started with Portal, but i want more games. Leave your suggestion please

Resident Evil DS. The WR is 26m45s now. But be aware it's a very optimized game.

You say you started with Portal... did you like speedrunning Portal and want something similar to that? Or did you hate it and want something completely different? Are there any particular genres you're interested in? What platforms do you have available to you?

All we have to work with is "under 40 minutes" which is far too broad for anybody to be able to give you a meaningful recommendation.

Watch some speedruns for games you like, or own, or are curious about, and see if any of them look interesting to you. Taking random suggestions from strangers who don't know anything about your preferences almost never goes anywhere.