a start job is running for... .md

Find and disable the service

Let the job be <X>

systemctl show -p WantedBy,RequiredBy <X>  

Let the result give some .service

sudo systemctl disable <Y>.service  

Example:

a start job is running for sys-subsystem-net-devices-multi-user.device

• Find the offending service systemctl show -p WantedBy,RequiredBy sys-subsystem-net-devices-multi-user.device
• Result:

  RequiredBy=wpa_supplicant@.service  
  WantedBy=  
  

• Disable the service:
  sudo systemctl disable wpa_supplicant@.service