It may be well-known but I recently re-discovered this free online Scrabble website. It’s great imo and plays well on laptop and iPad. You can play against the computer at several skill levels or against a friend or someone else online. I’ve only tried playing the computer.

These people also have a very cluttered iOS app which is appalling - literally a 30-sec ad after every turn. The website has a small unobtrusive ad near the top of the screen.