Dynamic Data Masking to anonymize data

I think you can use something like

Sum Value = SUM( 'Table'[Column2])

Show Value = 
IF(
	NOT ISINSCOPE('Table'[Column1]),
	FORMAT(
		SUM('Table'[Column2]),
		"#,#"
	),
	VAR CurrentTotal = [Sum Value]
	VAR Ranking = RANK(
		SKIP,
		ALLSELECTED('Table'[Column1]),
		ORDERBY(
			[Sum Value],
			ASC
		)
	)
	VAR Result = IF(
		Ranking <= 2 || CurrentTotal < 5,
		"N/A",
		FORMAT(
			CurrentTotal,
			"#,#"
		)
	)
	RETURN
		Result
)

Use the [Show Value] measure in your matrix and it will show values only when the value is >= 5 or the current row is not in the bottom 2 ranked by the value.

I think that the FORMAT functions are necessary because you can't have a measure returning multiple data types - e.g. whole number and string.