Hi there,
I would like to block the access to internet from a group of users. I have created a group, and try to block domains like [:alnum:].[:alnum:] (using regex) or . (using domain) . But neither seems work. Can you help? Thanks.
Rgds,
Pi-hole is designed to block things the users don't want to see (like ads), but it can be bypassed if an user desires.
Pi-hole (or any other DNS server) is not the ideal tool to block users. You need a firewall.
I think the most common way of doing this is not to use a Pi-hole, but to create a VLAN which has a firewall rule blocking outbound requests to those domains (and possibly other things like bandwidth, QoS or port limits). Put those users onto the VLAN by giving them a separate wi-fi login for it.