I think you have enough people here stating their pfSense / OPNSense works fine, so I’d guess you have something unique with your setup - maybe it’s a dodgy cable, or you’re running both In & Out traffic over vlans on the same NIC on your PC and getting problems with unmanaged switches dealing with that…

I had an issue with my pfSense box not negotiating to 1Gb on a Cat6 cable to a switch. I tried all sorts of diagnostics and it turned out to be a problem with the wall socket crimping, so hardware issues do need to be checked… I’m obviously assuming you didn’t use the exact same cables as your firewalla…

Just some different angles to think about…