util-linux v2.39 release has support for id-mapping

Well. Debian has ZFS 2.0.3, while Proxmox has ZFS 2.1.9.
Where There Is a Will, There Is a Way :-)
 
Where There Is a Will, There Is a Way :)
Of course. But Proxmox has also not replaced other important things like smartmon-tools with an up-to-date disk database. Yet we can still hope they allow this. Otherwise you could just build the packages for bullseye after it is available in SID. I backport a lof of important (for us) packages from SID to bullseye.

Debian has ZFS 2.0.3, while Proxmox has ZFS 2.1.9.
Yes, but Debian had no ZFS for a long time and the kernel is not Debian-vanilla, but Ubuntu LTS, but I get your point ;)