The 90/180 day rule has not been forced on Portugal. It has always been there for travellers from a foreign country.
It has not been ‘enshrined’ in EU law. It is a law passed by members of the Schengen Area by their democratically elected parliaments. Countries not in the Schengen Area agreement do not apply this rule but may have other requirements.
As above it is not a diktat from the people that sit in Brussels it is law of the country in which you are travelling if passed by their democratically elected parliament.
The fact that this rule is applied now to UK citizens is a diktat from the UK government issued when deciding to leave the EU after which the UK became a foreign country.
Many UK citizens owning property in Portugal did not register as resident despite warnings over four years. If they had, then as Portugal decided to honour these permits, all would be fine.
They are still available but require a different approach now the UK has left the EU.
It must also be remembered that even if you are registered as resident in the country where you have a second home the rule still applies but only for travel to another EU country for example if you are registered in Portugal and wish to visit Spain for more than 90 days then the rule applies to you.
Also remember to check if travelling to Europe where the country is not part of the Schengen Area agreement what the entry and length of stay requirements are.
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