I have read - but can't find the link (and as usual Civipedia sucks) - that Entertainment districts can be shared between cities up to 6 tiles away.
I found the districts 'cheat sheet' on a number of sites but it doesn't mention this.
Is this true - and can any other districts be shared between multiple cities?
If so at what tile distance - and is there a city limit within that distance? Are all benefits shared or only some buildings?
How can you check which districts are affecting which cities?