steps to repro:
1. create a new project
2. add a new assembly definition asset
3. select the assembly definition asset
4. in inspector, under Assembly Definition References, add a new list item
5. select the round button to open the selector dialog
6. in the dialog popup, double click an Assembly Definition to select it
7. click away from the asset
8. in the save dialog, choose "apply"

Expected: can double click an asset, changes are saved when choosing apply (from dialog options when clicking away from inspector without applying changes)
Actual: sometimes cannot double click asset to select, and changes are not saved when choosing apply

repro: 2021.1.0a3, 2021.1.0a2
no repro: 2021.1.0a1, 2020.2.0b9

Notes:
- ONLY repro on MacOS
- workaround for double click problem: open folder containing required assembly definition (without clicking off the assembly definition being edited) then drag and drop from project view to your new Assembly Definition References list item
- workaround for "apply" problem: instead of clicking off the asset, click apply button at the bottom of the inspector window
- workaround for "apply" problem: if you already clicked off the asset to invoke the dialog, click cancel to retain your changes, then choose apply in inspector