Hide future months in matrix

ROYMMM you should add a calendar dimension in your model which is a best practice to for any time intelligence based reporting, add month offset column in that table with datediff and month interval like below,

Month Offset = 
DATEDIFF ( Calendar[Date], TODAY(), MONTH )

Above column will make current month as zero (as of today feb 11, 2020), Feb 2020 will be 0 and Jan 2020 will be -1 and so on, and future months will be positive values, March 2020 will be 1, April 2020 will be 2 etc.

Now you can use this Month offset filter as page level or report level filter,  where month offset is less than equal to 0, and it will alway show current and past month and you can change this filter value as per your need.

Or with 2nd trick, using calendar dimension, as relative date filtering link here

All in all, you need calendar/date dimension in your model.