I tried to install as indicated in the github, but with such an installation it gives an error.
Fatal error: Uncaught Error: Undefined constant "COCKPIT_API_REQUEST" .
What version of Cockpit are you running?
Judging only on the error message, I think you’re running v2 and the addon you installed is most likely meant for v1.
Yes, my version is 2.2.1 and I trying to install this. Info about this addon is in oficcial v2 doc here at Layout type.
The layout field in v2 is part of the pro version. You can try it out for free during development https://files.getcockpit.com/releases/master/cockpit-pro.zip