What is the best approach to Block Gambling/Betting Sites using opnsense firewall?
Block it via DNS,
If you use unbound on the OPNsense or Adguard, just choose a block list that targets gambling websites.
Regards,
S.
OPNsense includes the Hagezi Gambling blocklist under the unbound blocklists. Start there, and you can also use any other provider you prefer.