After installing and configuring Omnivore for Magento 2, you end up with all your products in a "DEFAULT CATEGORY"

See below

This is due to a bug in Magento 2, whereby when we retrieve the categories for the store, the API does not return any data.

This bug was addressed in the latest Magento 2 version 2.3.4, so please upgrade to this version to resolve the issue.

It can be found here

Additional information: