Monthly Social Security Income and SS Medical Premium

Personally, I don't bother as the SS medical premium has no tax value for me, so I just have a scheduled automatic monthly deposit of the net.

If you want the full thing, then after referring to your annual SS letter detailing the amount of your medical premium deduction, including any IRMA, create a split transaction that starts out as a deposit of the net received.  In the split lines, create a line for social security income that is the total benefit as a positive amount, in the second split line, create a Medicare premium line that shows the deduction as a negative amount.  Record, then memorize and create a scheduled transaction for your future deposit dates - selecting the option to automatically enter the transaction monthly.

If you want to track your Part B, IRMA and Part D premiums separately, just create additional split lines.

Since the net of the split is positive, this is indeed a deposit. But, since it is a deposit, the expenses in the split get listed as negatives.