I found a different kind of problem, a serieshelpmate. I'm trying to get better by thinking outside of the box and solving different types of puzzles. So I found this one but I'm kind of stuck.
[FEN "1q4Nr/4K2k/8/8/8/8/1R6/8 w - - 0 1"]
Now, Black makes 5 legal moves without a reply from White. After that White gives a mate in 1. How? I am familiar with the rook and knight mate but I just can't see it.
(@NoamElkies found the source, with solution: Robert Pye, Irish Chess Union, November 2018)