The Navigation block has a hard-coded list of allowed inner blocks:

But plugins might want to add more blocks to that list. For example, WooCommerce could add a Product Search block or a minicart block (ie: a link to the Cart which shows the number of products in the cart).

If I'm not wrong, there is no way plugins can do that right now, so this issue is about making the ALLOWED_BLOCKS list filterable or introducing some other API so plugins can extend the list of allowed blocks inside the Navigation block.