Investors Consider Next Move as Signs of a Bubble Mount

For once, everyone seems to agree: Much of the market looks like it’s in a bubble.

Shares of unprofitable companies like GameStop Corp. and AMC Entertainment Holdings Inc. are rising at a breakneck pace, propelled by a growing army of individual investors.

Options activity is surging, bitcoin prices are near records and businesses are rushing to opportunistically sell stock through a flurry of initial public offerings, listings of blank-check companies and follow-on share sales.

To many, valuations look stretched as they hover at levels similar to the highflying days of 2000. That said, high valuations alone don’t necessarily mean the rally is near its end, investors say.

History has shown that markets have often been able to climb far longer than thought possible, be…