I do arithmetic problems. Not super complicated ones, but either unit conversions or guessing and checking cube roots or something similar.

I also imagine navigating places I haven’t been in a long time in a different way- I imagine a bouncy ball’s path through the building of my first job, or picture doing parkour through my elementary school (I’m not a parkour person).

I’m not sure if either 100% counts as stimming- I do both when I’m bored and have only begun to intentionally do the latter in stressful situations recently (it works beautifully though).

Not sure I'd call it stimming but deep thinking, jumping in rabbitholes or thinking about special interests is both typical and very soothing. I went into IT after my diagnosis because the amount of rabbitholes is just fun. I would say stimming soothes the brain when under stress or load. Deep thinking can do similar but can also cause stress and load which needs additional thinking. At least thats how I experience it.