hello and welcome ! ubuntu is releasing the 21.04 images in a few days (15 april is the release if i’m not mistaken). Around this time the version is basically 21.04.0 and after that it goes to 21.04.1 then 2 and so on.
you might want to try PureOS Byzantium (devel-v-10) in june or july around the time Ubuntu is a few months in this release or look at the LTS of ubuntu when in next changes it’s release number to see if anything of importance has changed with PureOS-devel image.
right now the PureOS-10-Byzantium-development image has been the same one since it’s release from november so that might be why you preferred to stay on the stable channel. there is also the bleeding-edge from Debian that is called “Sid” from the Toy Story character but that is probably too bleeding edge for you or me … 