MapleRead supports custom fonts!
https://www.maplepop.com/web/mr/help.php#pc_upload_font
So does FBreader in a similar manner.
If all else fails, I also use an iOS/iPadOS app called iFont that lets me load any font onto the Apple device as a system font. And voila, I have Bookerly and Charis SIL available to my ereaders that way.