I used to use portable mode more, before my Joy-cons started turning to shit (drifting, and also bad contact when plugged into the console itself). Maybe 20% of the time or so, back then. The most I used it in portable mode was in a family trip a couple years back, we spent a long time on the car and I set up the Switch on the backseat and played Hollow Knight that way. Those two weeks I was basically in portable mode always.
But nowadays, it's probably close to 90% docked, if not more.