Prior to OS X Catalina I could add a user to the sudoers by editing
/etc/sudoers with an admin account.
With OS X Catalina, I can no longer do this as it seems that Catalina moved to a read-only root filesystem and so
/etc/sudoers cannot be edited.
According to this official Apple User Guide, it appears that the sudoers file is now located at
/private/etc/sudoers, but I am still unable to edit this file with an admin account.
What is the correct way to grant a user sudouers access in Catalina?