Hi @thomas.billiet, and welcome to the Dato forum!
Unfortunately, tag-based invalidation isn’t something the Page Router supports by default.
I mentioned some possible workarounds in this recent thread that you can consider: Next Js getStaticProps and Dato CMS Cache Tags
But it’ll have to be something you write yourself, or use a library + external KV store for 
Alternatively, traditional mechanisms like ISR (incremental static regeneration) should still work well with the page router. Since your fetches in that model are defined by the page anyway, ISR will rebuild just that one page anyway and naturally invalidate all the queries that page needs.