If the measuring stick you use is getting shorter every year by design (monetary expansion/inflation) then you can be quite certain that the market will trend upwards for as long as you use that unit of measure.
S&P 500 growth has historically outpaced inflation by 6-7% annualized over the ~65 years of its existence. That cannot be explained solely due to central bank policy and/or inflation. Naive extrapolation would posit that keeping your money in this index would continue to stay far ahead of inflation given sufficiently long horizons [0].
If your goal is simply to keep up with inflation, then buy I bonds.
[0] The aphorism that comes to mind here is that "the markets can stay irrational longer than you can stay solvent".
I bonds are great right now. But you can only purchase $10,000 per year ($15,000 if you finagle your taxes right). I wish my IRA had an I bonds-like product I could invest in.
