As January 2021 comes closer for the British . I am aware that at high levels in the EU there is a certain exasperation that "all countries are ... etc etc "
UK citizens must NOT be special in 2021.
I will explain.
Bear with me.
1/

France has an affinity with ex colonies and granting access but is limited to granting freedom of movement to other members.

Portugal has an affinity with Brazil and tends to grant access.

Spain has an affinity to Argentina

NONE have an access to Freedom of movement within the EU.

ALL EU countries have a bar, a level. It is called "habitual residency ". It generally means "all or most of your income is derived and expended in THIS jurisdiction "

Being an EU citizen means those rules do not apply. Outside the EU means they do. There is a dgree of latitude between member states due to historical factors and tourism etc.
If you are allowed to retire in one EU country, you have NO rights in others.

It is complicated in law.
Some countries may insist one thing, others something different.
One thing is very real.
UK citizens MUST be careful in 2021. "allowed to be in Spain " no longer means "allowed to be in France ".

the complexity of dealing with 27 not part of 1.
They will learn .
It will hurt.
Fin