When you use the banner block in pagebuilder, you are only allowed to only select images when the UDW is opening up.

It should be documented how to limit UDW in this way when creating new blocks for with block attributes that opens the UDW ( locationlist and embed )

Hint : Limiting UDW to only allow images are done by overriding the template for the embed block attribute (vendor/ibexa/page-builder/src/bundle/Resources/views/page_builder/block/config/banner.html.twig) and make it open the UDW with a custom UDW config. So a custom UDW config is also needed.