IF And function more than 2 conditions

You can use && instead of AND, so your code would look something like this.

For further reading, here is a link to the DAX operator reference:  https://docs.microsoft.com/en-us/dax/dax-operator-reference

Hope this helps.

IF DATE([sap_insert_date]) = [Filter Date Validate]
    && [Validate Po Release Supplier] = "yes"
    && [Validate Source] = "backlog"
    && [Validate Po Approval] = "no"
    && [poa] !=""
    THEN "True"
    ELSE "false"
END

You can start with something like this:

CALCULATE
(
	[Your Measure]
	,FILTER
	(
		'Table'
		,'Table'[sap_insert_date] = MAX([Filter Date Validate])
		&& 'Table'[Validate Po Release Supplier] = "yes"
		&& 'Table'[Validate Source] = "backlog"
		&& 'Table'[Validate Po Approval] = "no"
		&& NOT ISBLANK('Table'[poa])
	)
)