It is current LTS version (doesn’t roll). Also and besides PureOS Live image you already linked to, here is link to Amber Plasma:
– PureOS-9.0-Plasma-Live_20200806-amd64 ISO in Hybrid mode.
And here are links to the recent PureOS Byzantium Live images (upgradable to the most recent Linux Kernel):
– PureOS-10~devel-Gnome-Live_20201120-amd64 ISO in Hybrid mode and
– PureOS-10~devel-Plasma-Live_20201120-amd64 ISO in Hybrid mode.
As I understand (just relying on my experience as user) Debian Bullseye is currently Testing, same as PureOS Byzantium (10~devel, by issue date let me guess that it is in Alpha 3 stage) so I’d expect that sometimes around/after June/July this year Byzantium will become Stable (weeks to count down, just speculating). Please remember this is just my thought, but I’d choose PureOS Byzantium Live image for install anyway (should be already, stable/mature enough, after apt upgrade of course).
As some kind of basic orientation (somehow related to your previous questions), this PureOS distribution(s) definition should help you further: