Hi @Guy991
We don't need to collect passport ID in the UK so are in a different situation to you.
If a guest choses to book in a country which requires accommodation providers to collect ID and refuses to provide it then they don't check in. Simple.
Presumably you tell guests on your listing that photo ID is required for any stays in Portugal. When you confirm arrangements with guest on booking do you remind them of the ID requirement. When you send your pre-booking confirmation if guests haven't provided ID explain it is a legal requirement for hosts to provide it in your country and if they aren't able to provide it they won't be able to check in.