This suggestion is related to this topic, https://beta.groups.io/g/main/topic/editing_photos_has_less/86042121 and I thought I'd create a new topic as I also have gone through the same issue before.
if you know the first letter of the wanted member's Display Name operating that key repeatedly will scroll through all those with that as the initial letter of their Display Name, ignoring all those with a different initial letter.
Still a bit tedious, but better than having to go through the entire list.
What would really make things easy/quick in using that dropdown (and possibly any same dropdown in other areas) is if it allowed slower typing of a partial or full name/address value with the subsequent full-value matching as you type, and/or an outright Ctrl-V paste and match.
It kind-of already "supports" both in a sense, as if one let's say is looking for username Peter (and for the sake of argument assume the group has only one), if they type that ultra-ultra-fast, it will find it right away. But it took me 5 tries to be able to type it fast enough so it matched right away, all it took was to either make a mistake or be too slow and it would now jump and match on the mistaken or slow-typed letter, so unless if all users have few-letter usernames and one is an ultra-fast typist, forget trying to quickly match on username, let alone email address. Trying to do a bunch of these owner re-assignments currently in a group with thousands of members can be time-consuming.
I don't know how much work it would require to make it match to the whole typed value as it gets typed, but I think just adding support for Ctrl-V pasting of a value after the dropdown has been opened should hopefully be easy and quick to implement, and it would make assigning the Owner instantaneous pretty-much, since when we mods assign/change owner we already know who it's going to be assigned to so we can have the pertinent (username or email address) value already copied.
Or alternatively, anything else you might think you can tweak or enhance in this dropdown that would help streamline things would also be appreciated.