I recently quite enjoyed this video[0] about beginning to decompile an old Lego PC Game I remember from when I was a child.

[0] - https://www.youtube.com/watch?v=MToTEqoVv3I

Marcel Vos has quite a few YouTube videos going into the mechanics of the Roller Coaster Tycoon games, especially taken to the extremes.

https://youtu.be/KVgoy_a_gWI

Here’s another great one on always beating Pokémon with the same set of inputs: https://youtu.be/6gjsAA_5Agk

Karl Jobst speed running videos

I recommend his video on speedrunning the first level of Quake, including an overview of the importance of Quake to speedrunning as a whole, and an explanation of Quake's movement mechanics that make getting a good time so complex:

https://www.youtube.com/watch?v=43d8fICz6gM

I don't care about speedrunning at all, but even I find his videos (particularly the Doom ones) immensely enjoyable.