More B2B design - this time a modal where a user can add and remove devices in a group. The challenge here was that the system needed to have capacity for 5000 devices. How do we help users find the device(s) they want to add to their group?

Looks great! How do you bulk add? (Checkboxes then ‘add’ button appears?)

Good question, this is an area I'm are still working on but currently there are two ways. 1) As you said, check one box, a section appears where you can "Select all" and "Add" - 2) When you apply a filter, an option appears allowing the user to add the filtered list. Have a look

Smart, I like it! You could try making the ‘add selected’ text the same size as the ‘1 selected’ text so they feel more balanced and cohesive :)