Unfortunately, I think ads is the most realistic way to go.

Sponsorships and/or donations would be a nice “beer money” bonus.

Subscriptions are PITA and too much hassle unless you’re doing them via some third party and they won’t bring a good amount of money at the “online daily puzzle in a browser” scale.

There are more exotic ways like licensing your puzzles to other sites, like online newspaper puzzle pages, Puzzmo is going in this direction IIRC.