How can I mark a key/favourite customer to always come to the top of the customers list? or add them to the bookmarks menu?

Hello Dorianburt, welcome to the Community page, thanks for sharing this question with us, but unfortunately, there is no way to mark a key/favorite customer or bookmark them in the menu, in QuickBooks there is no feature for this at present. However, we do suggest you leave this as feedback within the main cogwheel this gets sent straight to the developers. It will be a case of having to scroll down in the customer list to find the customer you need. You can only change the list in alphabetical order starting with (a) or ending with (a) by clicking the arrow next to the word name at the top of the list left-hand side.