I am saying that it is the HDMI connector that was causing the problem. Because it is old and a bit worn. It wasn't obvious because the screen still worked. But that was what caused 10-50% packet loss when 5GHz was enable on my router.
BT keyboard (apple) and mouse (Logitech), connecting via wifi (which surely you could deduce from my references to 5GHz bands - not sure why you are being so obtuse.). I *think* having soemthing (anything) pligged into the USB soc=ket next to HDMI proives a little extra sheilding but that is purely impressionistic.
I believe there may be a separate issue related to wired connection that just needs AVB/EAV to be disabled until you can get Ventura 13.2.1, but I have not tested that since, as I said, by problem was with the 5GHz band.