Posted: Mon Oct 12, 2020 9:09pm
Just to correct you on two small items: the first is that Britain has already left the EU. That occurred 31/1/2020. A transition period was allowed and that ends 31/12/2020.
The second thing is that the Withdrawal Agreement that was ratified last year is what covers our rights in Europe. Further movement of people is not being discussed in this round of talks. As at 1/1/2021, British passport holders become Third Country Nationals and therefore subject to Schengen stay regulations.
I’m obviously unknowing of what passport you hold, so this is not necessarily directed at you.
To the OP, if you are a British passport holder, after 1/1/21, there are only two ways you can spend longer than 90 days in the Schengen, of which Spain is a part - the first is to spend 90 days, exit the Schengen zone for an equivalent period, (90 days) and then return. You get 6 months a year that way, just with a 3 month break between the two three month periods.
The second way, after 1/1/21, is to apply for permanent residence as a Third Country National. Quite apart from the financial requirements, you would also need to spend no more than 10 months in a 5 year period out of Spain.
If you wish to spend only 6 months of the year here, then you would need to arrive and seek Residencia prior to 31/12/20, when the transition period ends. This will allow you to spend 182 days a year outside Spain. Be advised, to fulfill the requirements if continuous residency, you would have to spend 183 days a year here, which would then also make you tax resident (Spain then being your primary residency) - you would forfeit your Residencia should you fail to spend 183 days a year here.