I recently just upgraded to PureOS Byzantinum (see here) and have KeepassXC 2.4.3 installed now (just checked). I remember that this was not the case before upgrading, but don’t pin me down on exactly what version I had, I think v2.3.4 sounds about right…
Also: the blog post you are referring to is from about a year ago, so not that current.
You can always add one specific repo or simply install from source…