This issue happens when you had your profile initially set at 'Monitor' level that allows editing option only to Screen time, Mobile Apps and Networks. Then when you made changes to the apps section, the profile name changes to 'Custom'. As mentioned above, only Screen time, Mobile Apps and Networks options will be accessible at Monitor mode since this mode is meant only for monitoring and does not filter any content. If you wish to have access to all other options, please update the profile to some other level (Strict, Moderate or Mature) and it should work fine.