It is possible on the group page itself, for example if you search users on https://community.nodebb.org/groups/gamers it will only search that groups members. The front end doesn't have that option on /search though.
How to hide group members (or show title of hidden group)
is there a way to setup a group so that the member list is not shown on the group page?
I know of the "hidden" property, which hides the group as a whole in the group list and makes the group page not reachable. This would be OK if only it didn't hide group titles as well - so the question may also be "is there a way to allow users to display the title of an hidden group they're members of"?