NN group might have some resources, like this related article about all-caps: https://www.nngroup.com/articles/glanceable-fonts/

Or maybe more resources here: https://fonts.google.com/knowledge/readability_and_accessibi...

People tend to apply results from proportional font studies to monospace fonts. I guess monospace text isn't popular enough to get its own studies.

We need more readability A/B tests in general.