Of course, it can exceed $40,000 in 2021. Remember that in December 2017 the total (total) market capitalization was more than $750,000,000,000, now is $662.911.384.974, which means that a lot of money is being dragged from all the altcoins to inject that money into Bitcoin.
If a capitalization like the one at the end of 2017 is reached, I think there would be no problem in Bitcoin reaching $40,000 provided that said capitalization is not distributed among the altcoins.