Hard to explain bug. If you have yields disabled (y button), and you're trying to place a district, mousing over the city name will highlight all the yields (food, production) on tiles that you own and tiles that you can buy. If you remove the mouse from the city name, the yields on the tiles that you own disappear (as it should), but the yields on tiles you don't own yet - but are able to buy - don't disappear. Not even when toggling the show yields button (y).

I have the full version of the game (all expansions and DLC).

Screenshot: https://i.imgur.com/hgnbgGT.jpeg

No way to get rid of these yield icons.