Hi @CNT :
Firstly,let me explain why you encounted a delegation warning.
The point is datediff function is not delegable for CDS.

Secondly,I suggest you to use delegateable functions instead of Datediff.
for example:
Filter(Accounts,DateDiff('Created On',Date(2020,5,29),Days)>5)
is not delegable,but
Filter(Accounts,'Created On'<DateAdd(Date(2020,5,29),5,Days))
is delegalbe.(Because DateAdd(Date(2020,5,29),5,Days) is a constant, it does not involve delegation.)
Best Regards,
Bof