HOWTO: Stop "Finish your Chromebook Setup" pop-up from displaying

I recently added a new sign-in account to our Chromebooks for the kids. They had been using "Browse As Guest", but I've disabled now, that so that I can deploy the Chrome browser extension "BlockSite" to block an addictive game page (Nightfall) on the BBC website without blocking the rest of that website.

Normally I'd use a GMail account for signing into a Chromebook. That's  really easy (even setting up a brand-new Chomebook from scratch only takes 1 minute) but this time around, the kids already had an iCloud account, so I used that rather than giving them Gmail access - as I don't think 5-year-olds need email accounts.

It was nice to see that the Chromebook allows non-Google email accounts to be used for signing in.  As ever with Chromebooks, it was very quick to set up.  But there was one annoyance! Each time a new browser tab was opened, a small pop-up appeared:

          Finish your Chromebook Setup: [Try This] [Don't Try This]

Clicking [Try This] just goes to a pointless marketing page containing no functionality whatsoever.  Clicking [Don't Try This] makes the dialog box go away only to reappear next time you open a tab.

The fix as noted at https://support.google.com/chromebook/thread/10029131?hl=en is :-

Go to your Google Account.

Select 'Data & Personalisation' from the left hand side list.

Scroll down to 'General preferences for the web'.

Complete the 'Language', 'Input Tools', 'Accessibility' and 'Search Settings' 

I'm not sure how much you need to put in those fields, but anyway it makes the nag prompt go away.

One remaining annoyance is that user profiles can be deleted accidentally from the Chromebook login page without giving a password!  Only the owner's account is immune from this.