1. Create two sites, Site A and Site B
2. On Site A create a new Web Content article
3. On Site B add the Web Content Display widget
4. Navigate to Select Web Content Page and try to choose the article created in Site A
Filter and search is disabled, article in Site A cannot be selected
To be able to select existing article from other sites.
Create an article on Site B, then filter and search becomes active, so that you can choose the article created in Site A
Tested on master 8dd98dd