> I don't think this is due to the use of computers per say. Rather I think this is the influence of the 'Anglosphere' online both in term of culture and of tech (for example in Spanish autocompletion could insert the opening marks but it's probably often not even considered by the devs).

Indeed tech is not made in a local-friendly way normally - for example, losing those symbols is a direct consequence of the fact that they are usually buried with other rarely used symbols. But for cases like punctuation, I don't really mind it. It might just be me but I've never cared about " vs » and I'm happy to have an international standard to make things easier. diacritics are more important (n vs ñ, o vs ó) but those are usually far better covered by autocomplete, so no complains there.

ñ is not a diacritic, is a letter on its own, with a key on Spanish keyboard layouts.