Oracle Linux (gasp). They employ some of the main developers of btrfs, "their" distribution is just a RHEL rebuild with some patches (including btrfs), and it is very quick at delivering updates (they're usually several hours behind RHEL, while the next best — AlmaLinux — takes a day or two. Other rebuilds, very much including the somehow heavily hyped Rocky, are much slower).
I don't think there are many alternatives. OpenSUSE isn't supported for very long, and there really isn't anything else if you want btrfs, no Debian or its derivatives, and fire & forget kind of distribution.
Edit: Also look at Alpine Linux, if supports btrfs and has one of the best package formats that is an absolute joy to write (way easier than rpm or deb).
It's pretty different in some areas (no systemd and musl being two examples), check if that's fine for you.
I don't think they promise more than three years? (Not a criticism in the slightest, I don't demand anything from unpaid volunteers.)
"RHEL" is supported for 10, and if Oracle screws us over (I can believe in that possibility), ELevate lets you migrate sideways to any supported alternative.
I don't think there are many alternatives. OpenSUSE isn't supported for very long, and there really isn't anything else if you want btrfs, no Debian or its derivatives, and fire & forget kind of distribution.
Edit: Also look at Alpine Linux, if supports btrfs and has one of the best package formats that is an absolute joy to write (way easier than rpm or deb).
It's pretty different in some areas (no systemd and musl being two examples), check if that's fine for you.