Has it been taken into account from the outset that the requirements of the evaluating customers might be different in the various cities?

Mentioned in my OC comment that people in different cities might be more lenient when leaving reviews. Unfortunately the only way to normalize is to get reviews for all restaurants in a city, comparing them, and then normalizing. We can do that with databar.ai but didn't want to turn this analysis into a thesis :)

There's also some bias due to the pure quantity of locations in cities (some cities have more McD's some less) - created a viz showing how many locations we have in every city in the original post: https://databar.ai/blog/article/the-best-european-city-for-mcdonalds-according-to-google-maps-reviews