Need help with parsing API return string XML in Home Assistant templates

I am in the process of writing a MQTT integration for Home Assistant based on the “Template scheme” (based on Dr ZZZ’s). This a bit convoluted but does more than the MQTT lights in “Default scheme”. For Tasmota e.g. it gives me transitions if Home Assistant provides a transition time. This will also work with WLED.

I am just stuck with parsing the WLED API XML return string using Home Assistant templates.

Parsing JSON is quite straightforward, e.g. (example for Tasmota)
effect_template: "{{ value_json.Scheme | int }}"
but for WLED I need it to parse the value from in betwen <fx>value</fx>

Is somebody here in the know for how to do this?