I think that the previous ATH (20k) will be the strongest level of resistance since everyone will be afraid of repeating the 2018 scenario. Plus, we should not forget about those who bought bitcoin at the maximum price and when the opportunity arises, they will sell it in order to return their money back.
People were saying the same thing after 1000 dollars. I read that it's never going to happen again because it was all fake pump made by Mtgox willy bot and that all those bagholders who bought at that level will be waiting to unload if we ever come near that level. The truth is that all 1000 dollar bagholders from 2013 were long gone when we hit that level again in 2016 and 1000 was no resistance at all.
Perhaps you are right, but we should take into account the fact that these events, although similar, occurred at different levels of popularity and, most importantly, bitcoin capitalization. Therefore, this time everything can happen as I said.