Kimmy11 covered this off a few weeks ago ......
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This extract from https://www.gov.uk/foreign-travel-advice/spain/entry-requirements details the entry requirements to Spain after the Brexit transition period:
"Regular entry requirements
Visas from 1 January 2021
The rules for travelling or working in Europe will change from 1 January 2021:
you will be able to travel to countries in the
Schengen area for up to 90 days in any 180-day period without a visa as a tourist, to visit family or friends, to attend business meetings, cultural or sports events, or for short-term studies or training.if you are travelling to Spain and other Schengen countries without a visa, make sure your whole visit is within the limit. Visits to Schengen countries within the previous 180 days before you travel would count towards the 90-day limitto stay for longer, to work or study, for business travel or for other reasons, you will need to meet the entry requirements set out by Spain. This could mean applying for a visa and/or work permit. You should check with the
Spanish Embassy what type of visa and/or work permit, if any, you will needif you are in Spain with a visa or permit, your stay will not count towards the 90-day limit
The 90-day limit for visa-free travel will begin on 1 January 2021. Any days you stay in Spain or other Schengen countries before 1 January 2021 will not count towards the 90-day limit.
At border control for Spain, you may need to:
show a return or onward ticketshow you have enough money for your stay, anduse separate lanes from EU, EEA and Swiss citizens when queueing
Your passport may be stamped on entry and exit."
So unless you qualify for a visa or work permit, I'm afraid you will be restricted to Schengen rules of 90 days in a rolling 180 days.
Kind regards,
Kim