#16 - Between Quadruple Sudoku

 Between Quadruple Sudoku

Standard Sudoku rules apply.
Digits in a small circle must appear at least once in the surrounding four cells.
Digits on a gray line must lie strictly between the digits in the grey circles at the ends of the line.

Solve on Penpa: https://tinyurl.com/y8fy62ug

Solve on CtC: https://bit.ly/3NlIS4A