Something with serifs. Publico is my current font on Apple Books. Caecilia Concensed on my old Kindle.
Currently? TeX Gyre Pagella for Serif and Libertinus Sans for Sans. Both based on Zapf’s Palatino and Optima. Both readable, at least to me.
Atkinson Hyperlegible Next for Sans, Literata for Serif. I switch between the two every now and then to keep things fresh.
OpenDyslexic. It’s just super easy to read.
My Kobo’s font library is kinda sad, I miss the fonts I had on my Kindle. I tolerate Kobo Nickel- it’s the best of the worst! I just escaped the stifling Kindle ecosystem, I can’t go back!
Fonts on the Kobo are stored in /fonts. You should be able to grab favorites off of the LaTeX Font Catalogue and just copy them over.
I have been using Kindle for a while due to convenience, and I’ve been using the Bookerly font.
Great question though, I like seeing the options.



