For many years I exclusively used landscape. It was apparently logical because I’d used a PC on my desk at work for ±30 years. I could never understand why my wife always used portrait.
But hand size comes into it, along with the introduction of different sized iPads over the years. My wife’s hands are small and I have large hands. With the iPad Pro 11” I was able to hold it firmly, with thumb and fingers across the whole device, in portrait.
The iPad Pro M4 11” is especially comfortable for me. This is why, however tempting, I’ve never moved up to the larger screen.
Surfing the web, reading the newspaper, magazines and books is always portrait and landscape for YouTube along with films, TV etc.