Ok, so if that prediction is true what actions did you take?

Identify the therefore part of the prediction and enumerate the three highest priority steps.

Have you determined that the stock market will crash and bought positions accordingly? Have you sold all your nvidia stock? What are the implications in the broader economy and what steps have you taken?

I've thought about and asked this question. One potential idea: AI was sold as the "death of SaaS" and hit their share prices accordingly. If you think this is not true (at least in the near to mid-term) you could buy stock at (what you perceive as) a discount. I might look at a company like Constellation (a big vertically integrated portfolio of mature, decent revenue-generating SaaS) as a proxy for a fund focused on this strategy.

This sort of approach is pretty aggressive and definitely contrarian to the general market, but some alternatives to mitigate the coming pain (if you believe it's near) would be shifting into a more liquid position to take advantage of tightening liquidity, i.e. big companies may see their shares tank but will likely still be able to service their debt. In the meantime you'll miss out on a market that still seems pretty strong.

Recognizing a bubble and timing what will happen are two really different things. Will it pop tomorrow or 4 years from now? Will the market go up another 70% before the eventual pop?

I’ve got 15-20 years to retirement so I just watch the market but don’t do anything other than keep buying index funds and rebalancing periodically.

Do you have to? I'll be 45 in a few days, but even at that age, I'm still not expecting to need anything I have invested for at least 20 years, the ratio of the value of the broad overall market then to now is still likely to be a larger multiple than for any other asset class I can expose myself to. If there's really a bubble, maybe that won't be true in 5 years, but I've yet to see a downturn that didn't recover in 20. Even if your predictions are directionally correct eventually, if you're not clairvoyant, trying to time the market is still not a great idea.