Sorry to revive this old thread, but it’s the only one that seems to relate directly to what I’m needing.
Similar to Matthew, I need to change the label shown in the admin dropdown. I have many different users with the same First/Last name, so it’s impossible to know which user is being selected. I’ve tried using the ‘acf/fields/user/result’ filter as James described, but it doesn’t appear to do anything. Was this filter removed?
