Depends on your financial situation, age, tolerance for additional risk/losses and "need" for additional gains - eg: to meet your goals.
We don't "need" to take risk, so I've been selling. Sold roughly $10K today, in fact. Not a big sale, but I was up on one fund 17+% and the other 27% since 1/1/21, and I decided that was "enough" gain. It still exceeded historical gain averages handsomely, and I had no "need" to take additional risk with those dollars. So I locked in the profits before further erosion (which I see as VERY likely for a variety of reasons including pretty extreme geopolitical events and ramifications on our economy from them, coming into a Fed raising cycle and likely recession as a result, etc, etc) were to occur.
One thing you'll find here (and on Bogleheads) is an overwhelming preference to just "buy and hold" no matter what. That's great for some people, but I'm a big believer that prudent risk management is far more beneficial in preserving profits and meeting one's goals. Markets have had many periods of lengthy and painful downside in the past, and those periods tend to get glossed over as "no big deal". They can in fact be a VERY big deal depending on your timeframe and ability to psychologically live through them, particularly when you have no W-2 paychecks or other source of consistent income coming in. My general advice is - think LONG AND HARD about how you'd feel if the market were down 50+% and it took 5+ years to get back to even (which it did starting Feb 2001). If you can live through that - great! I can't, so I manage risk accordingly.
BTW, what I'm saying here is pretty heretical
and violates the Boglehead and ER "stone tablets from Mount Sanai" belief system in at least a hundred different ways. But you have to do what makes YOU comfortable and able to sleep well at night.
On the flipside of all that, be careful of "Anchoring" bias - that is, the tendency to say "but wait..I HAD X $, and now I don't". Focus instead on..does my current position meet my goals? And act accordingly. You may or not ever get back to $X. You may wind up a lot lower than $X. Or higher. But $X truly should not matter, psychologically painful as that may be. What matters is meeting your goals.