No, the "subsidy" or Premium Tax Credit does not apply to Medicare. It's only for health insurance from the Marketplace.
The Premium Tax Credit and what you are calling a subsidy are the same thing. The only difference is when you get it. You get the Premium Tax Credit on your tax return at the end of the year. The "subsidy" is called the Advance Premium Tax Credit. It's an advance payment of the Premium Tax Credit. You get the Advance Premium Tax Credit each month during the year. The advance payments are reconciled with your actual Premium Tax Credit on your tax return.