Hello Christoph,
Welcome to the Sonar community, and sorry for the long delay in answering you 
As you can see below, the rule supports a property allowing you to configure the analyzer so that it considers additional class selectors as valid:
In your case, you can just add the Vue.js 3’s :deep selector in the list of pseudo-classes. You will need to configure this change in your quality profile.
Hope this helps,
Yassin