Show MAX per month but only the MAX value

Tony2021 

Not sure I understood what exactly do you mean in first question, how do you create measures? In general it could be as many measures as you wish

To check earliest date with max amount for the company we may use something like

Max Amt:=
VAR biggestAmount =
    MAX ( Table1[Amt] )
VAR earliestDate =
    MIN ( Table1[Date] )
VAR maxAmt =
    CALCULATE (
        MAX ( Table1[Amt] ),
        ALL ( Table1[Date] )
    )
VAR minDate =
    CALCULATE (
        MIN ( Table1[Date] ),
        ALL ( Table1[Date] ),
        Table1[Amt] = maxAmt
    )
RETURN
    IF (
        biggestAmount = maxAmt
            && minDate = earliestDate,
        biggestAmount,
        BLANK ()
    )

Please check attached.