@rks I am not sure what you're doing when I see that extraction on the screen. I can tell you that, having installed both pfSense 2.4.4 and 2.5 on a 2011 Mac Mini server, it is possible. You should download the pfSense for flash drive, then get balenaEtcher for Mac and use that to flash the pfSense onto your jump drive ... you'll find that easy than trying to use Terminal which creates issues.
Once you have your jump drive with pfSense, connect it to your Mac Mini and boot it by holding down the option key while you're startup ... it will take a few minutes to boot fully. Once the installer appears, you can let the installer do the work; for example, format the hard-drive and install pfSense. Those thunderbolt adapter uses Broadcom NIC ... I ended up getting a used thunderbolt PCI enclosure and put in an Intel i350 NIC for IDS/IPS.