Travel is a red herring in Europe, IMO.
Quarantine can work in islands or if your country has low numbers and you can close borders + implement strict quarantine (even NZ and Australia had leaks).
Here, in Europe, we've missed the boat a while ago. We'd need to go lockdown again, plus keep strict measures.
We need to remember that travelling between Paris and London isn't that different from travelling between, say, Liverpool and London.
We need to have internal travel restrictions if we are to implement international restrictions.
The answer is to prevent transmission at most settings.
No point in quarantining travellers if masks aren't worn by everyone in shops and workplaces. Or if people from different households still mingle indoors, even if two at a time. You only need one infected person visiting 10 friends at their homes, without masks or distancing, over the course of a week to end up with 10 familial outbreaks. It could easily be 40 people infected. Who, in turn, just visited a few other friends and relatives, small numbers at a time.
Individual behaviours will have to change, like condoms for HIV. If you have multiple partners, wear condoms.
It's basically down to individual behaviour, most and foremost.