I've just installed KaOS for the first time and initial impressions are very good, the installation went well and the visual appearance is really nice.

The one thing that looks a bit odd though is the default bash prompt I get in Konsole which has empty square characters between the various parts of the prompt, see this screenshot: https://drive.google.com/file/d/1P2cCvH_sv9tgZwoGDS2TAy1_D5SVpt_2/view?usp=sharing where I've drawn red boxes around the bits I mean.

My .bashrc file has only a simple definition for PS1 so I'm not sure where this prompt is defined and what characters should be there.

Look closely at your bashrc file. It is not setting the prompt, it is using "powerline-daemon -q".
You can change this if you wish by hashing out the relative lines and unhashing the prompt line. By why bother.

You've found a bug in the powerline packaging, it has shown those squares a while, didn't pay attention to it, but it points to powerline not finding the needed glyphs (though the fonts are available in the powerline package).
I'll investigate what needs changing to get the proper glyphs showing again.

It is not a packaging issue, but rather the default konsole font. Dejavu fonts don't display the glyphs, either use the hack font, or any font with code in the name (like fira-code).
So, in yakuake/konsole edit current profile > appearance > choose font
With fira-code here now:

    At this point: The default theme in Konsole is also not ideal to read.

    Maybe we could change both?