In the list of vault items I can select the next item with Tab or the previous with Shift+Tab. But the item details only get shown when this vault item is selected by pressing Return.
This means: Without pressing Return item X selected but the details of a previous selected item are still visible - in my opinion a problem and a mistake (= item x is selected but the details of item y are shown)!
Im my opinion the closest way would be using the arrow keys 
and 
: But these keys just move the list up or down.
Feature request:
It would be nice to implement a way to jump to the next/previous item with updated content/details of the newly selected immediately (without using the Return key as described above). We see this correct behavior in many apps like E-Mail apps: or → the previous or next mail is selected → mail content of this newly selected mail is visible (without using any other key).
PS: I have not found any way in Bitwarden app (MacOS) to select the next/previous item and showing its details immediately. In case there is already a (hidden) way - great, then please let me know and this feature request ist obsolete.