30 days lock calculation

If you want the duplicate records to be counted as one value then use a this measure formula

Measure_CountRows = 
 Var _Cal=CALCULATE(Countrows(FILTER (
    ADDCOLUMNS (
        SUMMARIZE (
            ( Input ),
            Input[Category],
            'Date'[Month],
            'Date'[Year],
            Input[Updated_on]
        ),
        "StartDateMonthNo", 'Date'[Month],
        "Cnt",
            CALCULATE (
                COUNT ( Input[Category] ),
                USERELATIONSHIP ( 'Date'[Date], Input[Start Date] )
            )
    ),
    FORMAT ( Input[Updated_on], "MM" ) + 1 = 'Date'[Month]
)))

RETURN _Cal

Else use this to create a summarized table

Table = FILTER (
    ADDCOLUMNS (
        SUMMARIZE (
            ( Input ),
            Input[Category],
            'Date'[Month],
            'Date'[Year],
            Input[Updated_on]
        ),
        "StartDateMonthNo", 'Date'[Month],
        "Cnt",
            CALCULATE (
                COUNT ( Input[Category] ),
                USERELATIONSHIP ( 'Date'[Date], Input[Start Date] )
            )
    ),
    FORMAT ( Input[Updated_on], "MM" ) + 1 = 'Date'[Month]
)