At this moment you can only add text or an unmanipulated fields as a label in a block:
name: Heading
icon: title
label: "{{ blockdescription }}"
name: Heading
icon: title
label: "Some description"
This way, if you for example would like to use the label as a short preview you will also get the html codes:
name: Heading
icon: title
label: "{{ text }}"
Example: https://x.gnx.li/2jwqIu
It would be very cool and handy if strip_tags was applied on the label OR that you could use query language on the label so you can add a custom field method for manipulation:
name: Heading
icon: title
label: "{{ blockDescription.or('text') }}"
name: Heading
icon: title
label: "{{ blockDescription.customFieldMethod }}"