In chrome, if you ‘right click’ on an icon and choose ‘inspect’ you can spend days investigating all sorts of things.
The editor window is provided by a javascript plugin called Tiny MCE.
This uses a font to display those menu items.
In your case, the font is not loading … so defaults to something else.
The font-family is ‘dashicons’
I think it might be coming from the resource tinymce.woff
I think this is sourced from https://www.model-engineer.co.uk/wp-includes/js/tinymce/skins/lightgray/fonts/tinymce.woff
er… so it should be loaded from the same site as everything else (model engineer).
So I’m stumped. You have something local that is interfering with loading this font package from this site.
If you refresh page, right click inspect, go to network tab and filter on ‘font’ myave you get some clue?
Sorry… but might be interesting.

Edit… actually the font seems to be specified in dashicons.min.css?ver6.9
This specifies the url … but also seems to have an embedded base64 encoded font string as a src. So should even fall back to this embedded.
I really have streached the limits of my understanding now.
