If you are into self hosting already, you run a calibre web instance then you can enable full integration with the kobo so Your own self hosted eBook repository becomes the ‘store’ on the kobo.

https://brandonjkessler.com/technology/2021/04/26/setup-kobo-sync-in-calibre-web.html

I use it like to to get access to all my ebooks

If you don’t already do any self hosting, then it can take a while to get the foundation of your server setup. I already had that setup so this took less than an hour for me.

!selfhosted@lemmy.world

You can even self host a calibre web instance and have it fully integrated/replace the kobo store on the device

Kobo OS let’s me completely replace their store with a self hosted calibre-web instance for 100% DRM free ebooks.

Its fully integrated and organized exactly how I want