No, its not.
The transition point between the top (20%) and middle (15%; the bottom is zero) marginal rate of long-term capital gains rates are either exactly the top or bottom of that range for 3 of 4 tax filing statuses (you left off married filing separately, which is much lower than even the low end), but that’s not a “magic threshold” by any reasonable definition.
Its a threshold, but not one below which capital gains stops mattering, which was the significance falsesly ascribed to the “magic number".
If you had cited the bottom of the 15% bracket instead of the top as the magic number below which cap gains don’t matter, well, “magic” would still be overdramatic but you would at leaast have something of a point. But that’s close to an order of magnitude lower.
Sorry, but capital gains taxes start at $15,000.
Long-term capital gains less than $40,400 (or higher, depending on filing status) have a 0% rate.
In the US in 2021 (aka, right now) the magic threshold for capital gains is $445,850-$501,600 depending on filing status. So you're technically correct that $500k isn't a magic threshold, but it's certainly in the middle of it.
But more importantly, you're going down a technical rabbithole. The point of this comment chain is "what happens to people experiencing a one-time windfall capital gains of $500,000". The response was "what about RH investors". My point was they weren't making 500k, so it was irrelevant that they made income taxed as a capital gain. And I stand by that.