I saw Fiz's video about setting up Muck's splitter but when I try to turn on the autosplitter (mostly for run starts), it says there isn't an autosplitter for this game. Any tips?

In fact, I did not understand you, is there a problem with my video ?

Not an issue, but in the autosplitter video, there's an option for you to turn on the auto split function, but in my Livesplit settings, that option isn't available to me.

We now added in-game timer, check this out https://www.speedrun.com/muck/resources