May be you can play around this :
no #
in your json/href
"button" : {
"text" : "Scegli",
"href" : "contact"
}
{{ $anchor := printf "%s%s" "#" (anchorize .button.href) }}
<a href="{{ $anchor | relURL }}" class="btn btn-outline-dark mt-4">{{ .button.text }}</a>
And for anchor links, I guess using absURL doesn’t make real sense (see absURL function seems to eat HTML anchor-links)