There’s surprisingly many spots in the big cities (cafes, restaurants, malls) and also in the Shinkansen. That said, it can be kind of a hit and miss, especially if you leave the bigger cities.
Pocket wifi is overpriced IMO. eSIM with data-only is super comfortable and pretty cheap per GB. Get them in a tech store like Bic Camera.
However it may not be possible to create a hotspot. Regular data sim cards are also available and cheap. Not sure if they can have the same restrictions, or if those restrictions would apply to your phone.