We partly touched on the same topic in this thread already
I guess the question is: what’s the purpose of your question? Are you asking because you think the stock markets are overvalued and you want to know if it’s a good time to delay your investment? 
From my point of view it’s clear that the quick and fast recovery of the (US and worldwide) stock markets is due to QE. The FED was pumping money into the market at a rate never seen before. What would have been the alternative? To let the markets tank and risk an even bigger worldwide recession? I think a lot of the people in the central banks are much smarter than us wanna-be macroeconomic geniuses here in a forum.
Do I think it’s good and sustainable? Hell no! But I also don’t know what the alternative would have been in March 2020. I guess the central bankers learned their lesson from history (take 1929-1932 as an example where they didn’t interfere).