Perhaps these might make a great game more fun:
Maximize total score: Exactly the same rules as regular Scrabble, but focus on increasing the total score of all players instead of defeating the others. It’s subtle, it can be challenging for a good player, and it creates more magic and opportunity for everyone.
Keep it closer: A simple rule change changes the dynamics. If you’re behind in the score, you’re allowed to turn any of your tiles over and play it as a blank instead. This self-corrects as the game advances.
Points for bluffing: If you get away with playing a word that’s not in the dictionary, you get 100 bonus points. Now the game has social and risk elements as well.
Make it fast: My friend Joanna pioneered a version where you work to place all the tiles as fast as you can. The more you play from the shared pile, the more points you get. There are lots of variations, but you get the idea.
PS I get an enormous amount of pleasure playing this app. By playing against the computer instead of other humans, it’s calming instead of enervating. There’s also a button you can press to see what would have been your best move, which will really help your game going forward.