I’m looking for challenging hard mate in 2 puzzles to drill for improving calculation I’m up to lichess hardest difficulty and it’s not hard enough I want to be forced to calculate for more then 30 seconds. Any recommendations on phone please

I have been trying to implement things into my training that are not usually focused upon. While doing some lichess puzzles i realised i was particularly awfully bad at the puzzles that were about finding defensive resources. I do not think this is something unique to me, as most club level players (or chess players in general even) find more fun pressing or going Hail Mary against the opponents kingside with pawns and pieces. But it did make me think how can i learn to implement these things into my routine? There are atleast a couple of books on chess defense that i am aware.(And even those books for example Hellsten's talks about how few books there are on this topic) But resilience?

I mean think earnestly how many of the posts on here (including mine) are about opening choices, and which resulting middlegames are pleasant. But the practical skill of playing slightly worse positions arising through an inaccuracy or two is missing. I think that is one of the strongest difference between OTB play and online play, particularly higher you go. The strong players are much more better at playing strong moves while worse and that is why it can feel like a wall when playing up.

I am aware that certain things come through experience, however there still must be ways to tinker around with these in practice. For example an opening sparring that leads to a slightly better endgame for white, or taking a position from a GM game that was worse but defensible and was lost either due to time pressure and/or blunders, and then playing it out. More suggestions and book reccs are welcome!

For background my uscf dropped 80 points from 2160-2080 in the last 6 months and my fide 2050-1920. I am facing issues in getting hyper fixated on one idea and not being able to understanding the deep details of a position and instead playing quite fast as when I look at the board during the game it feels like the move is quite obvious but later I realize after turning on the engine that there were many more things to be considered. Lack of events are not the issue either as I get usually 3 decently strong events every month locally. This next year I am really hoping to improve as it is one of my last years of having a lot of time on my hands and so I can spend up to 20 hours a week on chess as I don't want to burn myself out either.