As the old saying goes, the market can stay irrational longer than you can stay liquid. So shorting a clearly overvalued stock can be a dangerous move.
In a world where seed and A stage AI startups are getting $100mm rounds and half that money's going to NVIDIA ... eh it's probably not too overvalued. I think there's more oomph left in the bubble.
When the valuation is something like "it looks like it's assuming they'll continue to sell $X billion a year" it can be reasonablish.
When the valuation requires "they will continue to grow sales X% a year" is when it quickly becomes impossible, and for a much smaller X than you might realize.