My test installation of OPNsense is connecting to 4 servers in various countries, USA (x2), Czechia, and Iran for reasons I can't identify. The IP addresses are 184.105.182.16, 89.221.210.188, 37.156.28.13, and 23.131.160.7 and connections are made about every 5 minutes. The installation is a vanilla install at this point, with nothing that ought to be polling for anything that I am aware of.
The only plugins I've installed are: acme-client (still disabled), maltrail, netdata, and ntopng.
Any ideas? I'm sure it's nothing, but I am mildly alarmed by this.
First step would be disable Plugins one by one. Maltrail e.g. updates trails via GitHub every now and then.
Could you share pcap to have look what's going on? Do you have any aliases defined with domain names that could resolve to these addresses?