I want to know, Can we sell Pinegrow build WordPress themes on ThemeForest or Codecanyon?
Sure you can.
You have to make your own design tho and not just steal someone else design and convert it to wordpress , that can get you in to trouble. So if you make your own design from scratch then you should have no problems with selling on Themeforest.
Just know that Envato is very “cliquey”, not friendly to new comers and very, very picky. There can be a a lot of money for those that make it in though.
Pretty much anything you create with Pinegrow you can sell. Though there are some copyright and licensing limitations to some of the bootstrap block components in Pinegrow so be mindful of that.