Adding fonts to Kobo eReaders is discussed here too:
https://www.mobileread.com/forums/sho...=197448&page=6
at post #78 and #82. (They're on page 6 on my monitor.) I had tried to install a font before but I missed the warning that when you add a folder called "font" to the root of the Kobo the "f" has to be lower case for it to work.
After re-reading those posts I fixed my Kobo and added Cloister Black (an Old English style font). It's a little bit of a challenge to read with it but it's kind of fun to read A Dance With Dragons that way.