That is one of the several forecasts from one of the major players in the US & global markets, see link below.
My FF forecast is SPX 3500 at the end of 2021, high SPX 4100, LOW SPX 3100
In the first three months following the February/March panic, assets from the Fed nearly doubled from 3.8 trillion USD to 7 trillion USD and then remain steady for the rest of the year. JPMorgan’s research estimated four different forecasts of where the Fed assets would be by the end of 2021; interestingly, JPM expects the asset to nearly double to 14 trillion USD in case the US experiences a L-shape recovery.
Even though we think that this forecast is very unlikely, the JPM research team assigns a low probability of less than 10 percent, with the base case being probably between a V-shape and U-shape recovery, leading to another 1 to 2 trillion USD of additional liquidity in 2021. The team sees the S&P 500 reaching 4,000 early this year with a base case S&P 500 price target of 4,400 amid the combination of constant liquidity injections and positive vaccine news.