Dutch Flat Mates (Minmax Quads): New variant to me creates an awesome Sudoku

Today's Video:

Immensely enjoyable fusion of rules that play off one another very well. Exceptional puzzle from Sujoyku

How's everyone else getting along?

Link to Play:

Dutch Flat Mates (Minmax Quads) by sujoyku https://tinyurl.com/SudokuSleuthDutchFlatMateMnmax

Rules:

Normal sudoku rules apply, i.e. each row, column and 3x3 box has to contain the digits from 1 to 9 once each.

Dutch Flat Mates: Each 5 in the grid either has a 1 directly above or a 9 directly below it. (It may have both, but it does not need both.)

Minmax Quads: Digits in a circle must appear in one of the four surrounding cells and either be the lowest or the highest digit in these four cells. (If there is no conflict with other rules, digits around a quad clue may repeat. In particular, the minimum and maximum may appear more than once.)