Paginated list of group members
If you are able to build an entity query for the group members you can use $query-&gt;pager(). See block to display nodes using entityQuery with pager

If not, you have to calculate the pager variables yourself. There is only one example for a pager in core that is not using a pager query, the taxonomy terms overview OverviewTerms::buildForm. Or you can use pager_default_initialize().

And a third and probably quickest solution is to build a view for the group members.