The Hidden Pairs technique is based on the same approach as Hidden Singles, but is a bit more complicated to implement. The technique involves analyzing notes in cells.
The main condition: if there are 2 cells with notes in a row, column or 3x3 block, and the numbers in the cells are not repeated in other cells, they can be made the main candidates. The remaining candidate numbers are deleted.
To make it easier to understand, let's look at an example with a 3x3 block. A close look at the notes shows that the numbers 3 and 8 appear twice and are not repeated anywhere else. These are our hidden pairs! We remove all other notes from these cells, leaving 3 and 8.
The "Hidden Pairs" method is considered advanced and is used by experienced players to solve complex Sudoku levels. You just need to learn how to use the "Hidden Pairs" method to solve Sudoku of any level of complexity.