TCP itself doesn't have packets with a size field though, it has segments. If speaking informally and everyone is on the same page, maybe it's OK to say. But this might be a good place to be pedantic, since there is confusion. The 64 KiB limit for TCP/IP is due to the 16-bit size field of the IP header. Crucially, TCP segments themselves don't have a size field (hence TCP only works over a lower layer that encodes size). TCP segments have a 16-bit window size, but that can be increased by TCP window scale option.
So TCP/IP has a 64 kbyte limit, but TCP itself does not. There was a proposed RFC for IPv6 "jumbograms" but that never gained adoption.
In the end, this 64k limitation being discussed comes from the DNS protocol itself where it encodes the length as a message prefix, this isn't related to TCP or IP.
In the end, this 64k limitation being discussed comes from the DNS protocol itself where it encodes the length as a message prefix, this isn't related to TCP or IP.