I've advocated for a good process to vet potential members before they join.
No action was taken - perhaps due to the vocal protests of a few who somehow saw it as a threat to non-Restricted groups?...
Maybe after the 'great YahooGroups migration' is over, January 2020?, a successful pitch can be made in the beta group (Groups.io suggestion box).
or
This is the workaround that I use:
/g/GroupManagersForum/message/20168