I personally have a setup using calibre-web-automated and koreader to store books on a server (laptop I put Linux on) and send them to the ereader with opds, but that’s a whole thing to set up.
Simplest way I can think of is get an epub off of Anna’s archive or zlibrary, connect the kobo to the computer with USB, move the epub to the device. Shows up no problem.
I personally have a setup using calibre-web-automated and koreader to store books on a server (laptop I put Linux on) and send them to the ereader with opds, but that’s a whole thing to set up.
Simplest way I can think of is get an epub off of Anna’s archive or zlibrary, connect the kobo to the computer with USB, move the epub to the device. Shows up no problem.