How to avoid systemd user instances from monitoring system units such as mounts and devices

Issue

• When a user is logged in, its systemd user instance (user@<UID>.service unit) is monitoring system units such as mounts and devices, as shown in the example below for root user

  # systemctl --user --type mount
  UNIT                          LOAD   ACTIVE SUB     DESCRIPTION                                                              
  -.mount                       loaded active mounted Root Mount                                                               
  boot.mount                    loaded active mounted /boot                                                                    
  dev-hugepages.mount           loaded active mounted /dev/hugepages                                                           
  dev-mqueue.mount              loaded active mounted /dev/mqueue                                                              
  proc-sys-fs-binfmt_misc.mount loaded active mounted /proc/sys/fs/binfmt_misc                                                 
  [...]