Dom0 update failed on v4.1.2 R4.1

You mean you lacked free disk space in your dvm template, not system memory?

Yes, what i wrote is perhaps misleading. I lacked free space in the template. The parameter i had to change is called “System storage max size”. It’s not in the dvm template but in the dvm’s underlying template “debian-11”. To increase memory in all derived templates you have to edit the underlying template.
The parameter that had to be set is found in the basic debian-11 template:

Template: debian-11debian-11: Qube SettingsTab "Basic"
section "Disk storageSystem storage max size:

Increasing the “Private storage max size” took no effect, i had to increase the “System storage max size” from 10GB to 15GB.

This affected the debian-dvm template from which the “update qube” (in my case sys-firewall) inherits. This is my understanding of the connections, in any case it now works like this.