This is my issue! All these years later, I am still not used to it, and I accidentally trigger multi-tap nonsense that I didn't intend because I am trying to click with my thumb.

My only point of reference is my MacBook Pro trackpad but I have no problem using my finger to move the cursor with my thumb resting on the trackpad and clicking. Not exactly the same because you lose some of the tactility of discrete buttons but it seems somewhat possible at least.

Yeah, most of the non-apple implementations of this don’t work with using a second finger to click in my experience. They expect you to click with the pointing finger.

Exactly. On ThinkPad touchpads with real hardware mouse buttons, I move on the touchpad with my pointer finger, and click with my middle finger.