Google Sheets Named Functions: DATEMAX and DATEMIN

DATEMAX(range)

=
ARRAY_CONSTRAIN(
  SORT(
    FILTER(
      range,
      MAP(
        range,
        LAMBDA(
          cell,
          ISDATE(cell)
        )
      )
    ),
    1, FALSE
  ),
  1, 1
)

DATEMIN(range)

=
ARRAY_CONSTRAIN(
  SORT(
    FILTER(
      range,
      MAP(
        range,
        LAMBDA(
          cell,
          ISDATE(cell)
        )
      )
    ),
    1, TRUE
  ),
  1, 1
)