FB and GOOG have been hoovering up practically all growth in the digital ad space. Those PE ratios are high, but they have been blowing out their earnings quarter after quarter.
FB has 2.07 billion monthly active users, about 1/3 of the world population, with significant user engagement. Their userbase is on par with major world religions and continents.
Google is the same, though their engagement is a lot more fleeting.
Amazon is hoovering up almost all of the retail growth in e-commerce, and is now extending beyond e-commerce. They to an absurd extent, try to match their R&D and capital investment to their revenue and almost operate as a non-profit, so their P/E ratio always looks absurd, but their book value has increased tremendously over the years.
This isn't 1999 where like Tesla, there was no P/E ratio because there were no earnings (profits), and in the life of the company there had never been a single dollar of profit made, and companies were often rated at 50x their revenue numbers!
These are companies that have shown sustained revenue and profit growth. You can call them overvalued, but this is not in my opinion a bubble, and I think its important you understand the difference between now, 1999, and 2007 or you won't recognize the next one when it comes. In 1999 there was an absolute mania over .com stocks. In 2007 we had a credit bubble that was clear in many statistics and being shouted from the rooftops by some that was impossible to sustain and accompanied by speculators flipping houses, phrases like "buy now or be priced out forever," and other nonsense.
Today, while there are some high P/E ratios, they are at least backed up by long periods of sustained growth rates. Of course it can't last forever, and one can only hope that they will gently reduce their growth rates and have a soft landing rather than a hard crash.