It is not possible as you think as which whitespace characters are displayed with other characters can't be configured.

But with syntax highlighting it is possible to

• add the non-breaking space character to list of delimiters, i.e. to line starting with /Delimiters = and
• add a color group only for non-breaking space (or for common ANSI characters) and
• add to this color group just the non-breaking space (and other ANSI characters) as "word" (string to highlight) and
• selecting for this color group a different background color than normally used.

This results in getting all non-breaking spaces (and other common ANSI characters) highlighted with a different background color in the file syntax highlighted with the syntax highlighting wordfile containing this definition. I use this now in my wordfile for HTML for the non-breaking space, the En dash and the Em dash.

A non permanent highlighting of the non-breaking space could be achieved with:

1. running a normal find with the non-breaking space as search string or a Perl regular expression with \xA0 as search string and having find option Highlight all items found selected which works only if persistent highlighting is not disabled in configuration;
2. running a Quick Find with the non-breaking space;
3. selecting a non-breaking space and clicking on View - Highlight All Selected (requires UE v22.10 or UES v15.20 or any later version).