Doesn't FreePBX use their own distro though? Or is that something different?
I don't know. I was always under the impression it was CentOS, which until recently is the same as RedHat Enterprise Linux.
I'm sure @JaredBusch knows more.
FreePBX is Sangoma 7, a fork of CentOS 7.
They had a private alpha of FreePBX 15 or 16 built on CentOS 8 that was never public. That was killed when RedHat killed CentOS 8.
FreePBX 16 is still Sangoma 7, but with PHP 7.4 ported in and a few other updates.
There has been no announcement yet, but a few threads on, choosing a new fork to go forward with.