Well, why do you want to play?
If none of the challenges seemed interesting, I have to wonder what you DO find interesting? You don't have to do a current one, you could do an old one just to challenge yourself.
I had a similar issue, when I used to play years ago - I found the cheats to get money and then it quickly got boring. What was the point? So you have to figure out why you want to play and what you want to do.
I like to make a family that is just like my husband, myself and our toddler, then achieve things in the game we want to IRL. It's motivating.
I am also doing 2 of the current challenges and a Dynasty.
If you think some of the dynasty rules are too hard, do an unofficial one.
Read the stories people have done and see what you liked about them. Write a story or just play.
But the game is most interesting and fun when you A. don't cheat and B. have a goal. Maybe the goal is simple, maybe it's hard. Maybe you want to see if you can achieve a LTW and keep your family poor, maybe you want to make a ton of Simoleans without cheats, maybe you want to build a fancy house, maybe you want to punish your sims.
Pick traits you've never played and try them. I always used to pick the "positive" (as I saw them) traits and then one day I made an evil, insane, daredevil Sim. I found SO many new things about the game. When I started making up stories about my Sims I grew to love them.
If nothing sounds fun, then maybe it's time for a different game or hobby. MAYBE pick something the Sims can do and try to do it in your real life
Ever painted a portrait before?