The puzzles on chesstempo are much better but the interface is much worse, particularly on mobile.
Honestly the puzzles on chess.com are better than lichess. The lichess ones just seem to have limited scope, I'm not sure why.
That said the interface is good and if you're finding them too easy then your puzzle rating should be rising to the point where it's offering you puzzles you'll find more challenging.
I feel like most of the chess.com puzzles have a point: fork the rook and king with the knight, or exploit a pin. That makes them easier (or maybe my level isn't high enough there, yet). The lichess.org ones I often have no idea what to even try, and when I'm given the solution I still don't know why it's the best move (though looking at the "Spectator room" of the game can help). Sometimes the better move is only marginally better; like the computer assesses black as -3.4 instead of -3.6.
Honestly the puzzles on chess.com are better than lichess. The lichess ones just seem to have limited scope, I'm not sure why.
That said the interface is good and if you're finding them too easy then your puzzle rating should be rising to the point where it's offering you puzzles you'll find more challenging.