How do I change the font in RIDE?
RIDE is essentially a Chromium web browser and fonts are controlled by CSS.
so if you could find the CSS file
style/ride-base.css in your installation (for example
/Applications/Dyalog.app/Contents/Resources/Dyalog/RIDEapp/style on macOS), you can modify the line that defines
apl font family to the font that you desire.
Or you can
F12 in RIDE to open the web inspector to test out the font on the fly.