You can use OR in a search also.  There is an outstanding issue with the search strings though (see https://beta.groups.io/g/main/topic/71860654) and it can help if you put your search string in quotes. Searching for something like "Smith" OR "Jones" OR "Harris" works fine for me.

Indeed, [ Smith OR Jones ] works in the Members search box. But I had tried "OR" n the Direct Add page search box of a subgroup, and there it does not work when trying find either Smith or Jones as an un-added member. This may be a bug and I will open a new topic for that.

Dan