copy/paste from my post in the other thread:
For the books I have bought from the Google Play store, I buy and download from my PC then sync to my reader using the Reader for PC software (software is still available for download from Sony
https://www.sony.com/electronics/sup...loads/W0010082 ). I assume you can do the same for Kobo books.
I don't actually buy a lot of books (I read mostly library books) and I don't think I've actually bought any from the Kobo store. I do have books bought from the now-defunct Sony store which were transferred to Kobo at the time the Sony store closed, but those books were already all on my reader beforehand.
I have received a number of Google Play gift certificates as birthday/Christmas gifts over the past couple of years so that's where shop for ebooks.