Ok, thank you, I will try to add some fonts and report back.
*update* That is the folder I tried adding fonts to previously. I've added some more now, but I can only select "Libertinus Serif".
I've rebooted my device to make sure it wasn't an issue with cache.
I'm not sure how to make a screenshot of my Kobo screen, but I expect you can imagine what a selection box with one font looks like
Any further suggestions would be greatly appreciated.
PS. Your screenshot of the folder does not show the fonts in your selection popup in Plato, what gives?