Which cities offer the best work-life balance?

It depends on what kind of work you do obviously.

That's really hard to tell, with so many countries or parts of countries still locked down 

I doubt that the cities that ranked highly pre-pandemic will get any worse after.  As to what changes we'll find when (and if!) we reach a "new normal", my crystal ball is still pretty cloudy.

Strange to see the cities as an option for the work/life balance. In my opinion the main category here is the work, and respectively the company. If this is wisely selected, then you will have free time for your personal life, less stress and enough money to invest in your life.

You can travel to a different city every weekend(if you can afford this), but cannot change your job often.

For me the better balance is not in the cities but in smaller towns / villages. Less rush and bustle, more relaxed, friendlier locals.

I greatly improved my work-life-balance since switching to an employee-friendly employer and changing my working hours to 80% (four-day work week). This does not depend on the location, but it is difficult to find employers who are supportive of such ideas, anywhere!
I am glad to now have far more time for my family, to increase my engagement in social causes, to manage our several rented-out properties and I am even guest lecturer at a nearby university.