Last I heard from the registrar was that they’re getting the error “Nameservers list […] different from NS Records: […]”. That’s exactly the same error as in the linked threads, which is why I ended up here.
Apparenty *.it domains do some kind of validation and won’t accept NS updates if that fails. – thats also what my registrar told me.
I’ll get back to them if you could confirm that the NSs shown in the UI rn are indeed matching the server side config, asking them to give it another shot.