"Disk not ejected correctly" msg from 2016 MacBook laptop
If I remember correctly, to completely get rid of the message, you can go to System Preferences -> Energy Saver and uncheck the box that says "Put hard disks to sleep when possible". That will eliminate the message, but it also means that your computer will use more energy and that the hard drives will be on and spinning constantly.

If this doesn't work, let me know. (Disclaimer: It's possible this won't work; I can't remember if "Put hard disks to sleep when possible" works only for internal drives or also for external ones.)