This is a favorite topic of mine. There are several multi-country metropolitan areas in Europe, for example Malmo-Copenhagen and Görlitz/Zgorzelec. Many cities have smaller suburb cities across the border, like Strasbourg-Kehl and Geneva-Annemasse. And the Benelux countries take this to the extreme, of course.

Even Berlin, which is pretty far from the Polish border, have commuter trains to Poland. That's right, the Berlin metro ticket will take you to Poland.

I live in Spain and Switzerland. I spend most of the summer in Spain, and the rest in Switzerland. I work 100% remotely, so I can live and work anywhere (not seamlessly, as I need visas and residency permits and everything else, but still doable).

My wife is a scientist, so we travel a lot and change places of living. So far, I lived in Russia, Switzerland, Italy, Spain and Denmark, and about 2 months in the US.

As a young adult, I studied in a country (had a flatshare there) and took the train (2hrs) at the weekend and during the holidays to stay with my parents. I guess lots of people close to borders know family situations like that (parents, partners).

Now, I have a job with 90% business travel between two countries (but same cities). Have small apartments in both. It is just more economical and comfortable that hotel room living.

There are also often reasons not to completely move to a country, even if it's close (different tax situation, having to switch social security systems which affects your retirement, wanting to stay inside a certain social security systems which requires a place of residence..)

you can live in Bratislava which it's less than hour drive from Vienna where you can work every workday, plenty of people in Europe live nearby border and spend lot of the time on both sides speaking completely different languages

Working at CERN is one example