Well, there are many discussions about ligatures in this forum.
The engine used for Kobo Epub (the ones You get if You buy a book from Kobo, or if You read pocket articles, or if You sideload from calibre in this format) ACCESS has no ligatures in default mode. You can enable them by patching Kobo or modifying css of the book but You will have some rendering issues.
The engine used for epub, RMSDK, has ligatures, so You can side load an epub and get ligatures.
You can also install Koreader and/or Plato that both support ligatures.
https://www.mobileread.com/forums/sh...=256757&page=2 (from #19 onward - Not all the various advantages of one of the two engines discussed in this thread are still effective, it is a 2015 thread, but nothing changed about ligatures)
https://www.mobileread.com/forums/sh...=313876&page=2 (from #18 onward)
I discussed in the second thread the argument a few days ago, and I was invited to see the first thread. But looking around the forum You will find much material.