To fix the lpadmin popup on macOS you will need to add your users to the lpadmin group on the macOS system. Here is a guide on how to do this.
1. Open Terminal. You can do this by searching for “Terminal” in Spotlight or navigating to Applications > Utilities > Terminal.
2. Run the following command to add a user to the lpadmin group:
sudo dseditgroup -o edit -a <username> -t user lpadmin
sudo dseditgroup -o edit -a john -t user lpadmin
Once you have done this you should no longer see a popup in macos asking for credentails