I use the coloured flags to be able to find card with specific criteria. Sadly, the old flag colour is overwritten by the new one, so I cannot have multiple. For example, I want to mark that I don’t understand the solution of the card, but it should also be marked in another colour so I can find it easily to be able to write the note on a piece of paper I am allowed to use in the exam.
So it would be great to be able to select multiple flags. Clicking the flag could bring up all the flags like it is already, but then you could click on the flags you want to add or remove them by clicking if they are added currently and confirm your choice with a button.
Also, maybe it would be a good idea to split the flag colours in the card overview to be able to see all the activated flags easily.
I could alternatively use keywords, but adding or deleting them takes more time than just clicking the flag symbole and the flags you want.