In general the Android and iOS apps from same companies as sell eink ereaders are not the same. I doubt Kobo eink models do readium for kepub and they use an older RMSDK (ADE 3.x?) for epubs. If renamed to use the kepub renderer there is more epub3 support. An actual kepub has extra kobo spans and annotation/highlights fail on a simply renamed epub.
Amazon Android and K4PC (and Fire which is basically Android) will let you have Amazon Kindle ebooks with features that don't work on eink Kindles and can't be bought for them.
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