What's the issue you had? When you reboot or quit you're kicked back to regular Kobo and you open up Koreader through a menu option.
The Kobo OS is good enough for me to recommend it to family, there's nothing wrong with the iPod experience of uploading books.
But Koreader+Tailscale+Kavita OPDS is the best reading experience I've ever had.
I don't remember frankly, maybe something with the script, maybe something with KFMon. Lack of integration with the Kobo OS itself? Maybe it had to be rooted to install KFMon, but I was reading Koreader could just run inside nickel menu maybe? But yet the script installed KFMon?
Again, I don't remember. And whatever it was it's not worth me trying to reinstall it just to remember what it was, and then to uninstall it again.