It's not new, but it's newer than 5.4, which is what mint 20.3 uses by default. I'm experimenting with 6.x and may upload an ISO with that in the future.
Nice, yeah a 6.x would definitely make more sense. 5.15 is two years old now, and personally, as an AMD laptop user, 5.x lacks a ton of useful features, especially around power saving and performance.