[Vuejs]-Using grouped prismic link fields in a vuetify v-btn properly?

Your syntax is wrong, try this snippet:
<v-btn :to="section.link">Link</v-btn>. Also <b-btn></v-btn> has not router-link prop. Just pass prop to. If you pass to prop, it implies that you want that button to be a <router-link>

Denotes the target route of the link.