cant find the forward earnings chart, but PE is close proximation
https://www.macrotrends.net/2577/sp-500-pe-ratio-price-to-ea...
The dotcom bubble peaked at around 46, while we are currently at 30. Will it grow? Who knows. But the bubble certainly isn't as big as claimed by the grandparent comment.
PE ratio spikes are a lagging indicator though. The spikes are after recessions.
Markets collapse, investments slow/stop, orders dry up, suddenly stocks must be valued on future hypothetical orders post-recession (same company, eventually the economy will turn and someone will buy), current PE values spike as current earnings become decoupled from stock price