ETIAS for residents of Schengen countries?

I am aware that UK citizens will need to pay €7 for an ETIAS Visa from around November this year to be able to travel in Schengen countries.

What is the situation for UK citizens registered as residents in other countries, such as here in Spain?

My previous understanding is that the 90/180 rules applies to us as soon as we exit Spain into other Schengen countries. Entering Schengen from UK/Ireland means everyone has to go through some form of entry control, but living in Spain means we do not have such checkpoints, so it is quite easy for them to monitor entries from outside the Schengen zone.

How, in practice, is the ETIAS system enforced/monitored for people already resident in Schengen, where there are no internal passport checkpoints. If I drove to France, for example, how would they know when I had left Spain?

Would we have to buy an ETIAS Visa before we drive across to France, even though there would be no physical border? Do we have to register anywhere to say where and when we enter other Schengen territories due to the fact there are no checkpoints?

This has been discussed (several times) . Those holding a resident card from a EU country will not require an ETIAS.
The 90 in 180 rule does not apply to those holding resident cards from an EU country. Just the 3 months stay without registering in another country applies. 90 in 180 only applies to non EU residents.

You can spend 90 days in, say, France and then 90 days in, say, Germany. You do not have to be out of France for 90 days after your initial stay as you are already in the Schengen area and no 90 in 180 applies.

The only thing you'd need to be careful of is being out of Spain for too long in your inital 5 year temporary residence.

Thanks for clearing that up. I was not finding info about residents, just references to the passport they held/citizenship.

That is really useful then, we can enjoy the continent without much in the way of restrictions.