How to convert Extended Event action mdmget_TimeStampUTC to datetime?
The value 132085458320550473 is the number of ticks since January 1, 1601. Use the below function to convert it to datetime:

CREATE FUNCTION dbo.ConvertTicksToDateTime ( @Ticks bigint )
  RETURNS datetime
AS
BEGIN
    DECLARE @DateTime datetime2 = '16010101';
    SET @DateTime = DATEADD( DAY, @Ticks / 864000000000, @DateTime );
    SET @DateTime = DATEADD( SECOND, ( @Ticks % 864000000000) / 10000000, @DateTime );
    RETURN DATEADD( NANOSECOND, ( @Ticks % 10000000 ) * 100, @DateTime );
END