Might I suggest:
https://www.mobileread.com/forums/sho...d.php?t=226456
And unless you want to allow Kobo to process your large library, you should put your Library into a hidden folder. A hidden folder for this purpose in Linux is a folder that has a leading dot/period. (.Library would do) To make such a folder for your MicroSD card, on a Windows machine, just name the folder with a dot/period on both ends (.Library.) and the trailing dot/period will disappear leaving (.Library), which Linux will see as hidden. So, Kobo's software will not process all those files that you will have in the folders inside the .Library folder.
If I were you I would do a factory reset to undo that 8hr+ of processing and then install the alternative readers on a clean system.
Luck;
Ken