to figure out if he is into me.
Based off the background you wrote and the one screenshot you uploaded, he doesn't seem very enthusiastic about you. He dismissed your invite and doesn't go along with your playful vibe.
However, there might be some context I'm missing. For instance, maybe he just needs a day to himself or hitting the gym on Sundays is his routine.
In conclusion, you probably don't have enough information to know for sure whether he's into you. It will help you figure him out if you don't initiate as much or invite lees, to see if he takes initiative.