[hollerith]

Which IDE or editor are you viewing this proportional font in?

A proportional font in Emacs doesn't look right to my eye. My guess is that there are subtleties in the spacing between letters when a browser or a book publisher renders the text that Emacs does not know about.

[accelbred]

Emacs should also be doing kerning. I use proportional fonts for non-prog-mode buffers and no issue here.

[evertheylen]

Just VSCode, or more specifically, code-server (https://github.com/coder/code-server)