SQL window functions provide extremely powerful and useful features that let you work with observations more easily. Different types explained here.

DATEDIFF is a common function in the SQL Server to find the number of days between two dates. Oracle offers its own solution, although does not have the DATEDIFF function.

When I switched the compatibility mode to 150 (using SQL Server 2019), the same query took 900 milliseconds and the execution plan showed all of the detail of the function's execution.