A puzzle format that has me very interested is variant sudoku. There are many varied rules and constraints to follow and there always seem to be more every week.

In this example from Four Corners from Rätselportal the rules are

Normal Sudoku Rules Apply.

Renban Lines: Digits on a purple Renban line must be a set of consecutive non-repeating digits, not necessarily in order.

Whispers Lines: Neighbouring digits along a green Whispers line must have a difference if at least 5.

Region Sum: Cells on a blue region sum line are divided when the line crosses a boundary between boxes. Each region on the line must sum to the same value.

Quadruple: Numbers in a white circle must appear in the surrounding cells.

Palindrome lines: grey Palindrome lines must contain a sequence of numbers that is read the same forwards and backwards.

Diagonals: Digits cannot repeat across the thin black lines on the diagonals of the grid.

If you want to try it out you can attempt it here https://app.crackingthecryptic.com/z34jhemb4n

Other sudoku variants that I have solved are available here Puzzle I have solved on Logic Masters

The reason I got into these puzzles was stumbling upon this YouTube channel. Cracking The Cryptic. I would also highly recommend watching BremSter