@bug-meister Nope. This is not Jinja nor any other kind of templating engine. This is a simple search-and-replace kind of implementation and is limited to name and %, the later being VM index. From the docs:
Xen Orchestra offers the ability to insert variables such as the virtual machine name {name} or a virtual machine index %. However, the expressive power is limited to the graphical interface. For instance, it is not possible to build a series of virtual machines with complex values or from external data.
Reference:
https://docs.xcp-ng.org/guides/create-use-custom-xcpng-ubuntu-templates/
In other words, there is no advanced templating of cloud-init configuration but you could probably template it outside XenOrchestra and apply it via Terraform:
https://registry.terraform.io/providers/vatesfr/xenorchestra/latest/docs/resources/vm