I'm having this problem. For instant/manually triggered flows, the amount of Team members I am allowed to read in is up to 50,000. For scheduled flows, that number maxes out at only 5,000.
The error I'm getting is "Flow save failed with code 'InvalidPaginationPolicy' and message 'The pagination policy of workflow run action 'List_group_members' of type 'OpenApiConnection' at line '1' and column '5047' is not valid. The value specified for property 'minimumItemsCount' exceeds the maximum allowed. Actual: '15000'. Maximum: '5000'.'.".
It seems that you need a plan for power automate to do this. Which one?