Ok, my solution for now is following: created ACF repeater for taxonomy. Loading it in a loop in custom metabox on edit post page. For each key metabox is creating input with name=field[key], saving all inputs as array metadata into one metakey=>value. Loading works, saving works, displaying also. It’s not really using much of ACF (only repeater for category), but I guess it’s the only way now.
If anyone has better solution, I would be glad to hear it.
