How to disable "x days since last backup" reminders in High Sierra

Since I updated to High Sierra (Version 10.13.1 to be exact) the "x days since last backup" reminders have returned, showing up every day or so in the top right corner of the screen. I checked, and the Back Up Automatically box in System Preferences is still unchecked.

Is there any way to make the reminders not appear again?

I'm not interested in backing up using Time Machine tool I've had poor success restoring my computer with it one previous time.

I had the same problem - you have to have your back up disk installed / mounted. Then 'Select Backup Disk' from System Preferences / Time Machine, choose to 'Remove' - this way you force it to forget the disk and so it no longer reminds you about 'XX days since last backup'.