I am a UK citizen who now has residence in Spain, which is part of the Schengen area of (more or less) the EU.
Since Brexit I have been able to travel between the UK and Spain and vice versa by showing my UK passport and asking the Spanish border officials not to stamp my passport with entry and exit stamps, which if I show my Spanish residence card, they are happy to do.
I normally fly directly between the two countries. However I wonder if I may encounter difficulties if I drive from the UK to Spain via, for example, France and then make the return journey Spain-France-UK say five years later. Would the French Authorities think I had overstayed my 90 day non-visa visit to the Schengen area?
And would the ETIAS scheme make any difference?