As Peter said no TTS, and while I’ve not tried it there is some support for sideloaded audiobooks, though you won’t get the same experience as with Kobos own audiobooks. And unlike sideloaded ebooks the features missing have a pretty good chance of being something you will miss.
See here for more info on audiobooks and sideloading:
https://www.mobileread.com/forums/sh...d.php?t=342747
Note that Kobo has never officially stated this is supported. It just works as is right now. And while most things that just work either continue to work or get improved upon there is a chance it’ll stop working in some future firmware.