I have yet not plugged my LAN PC directly into my cable modem. There was no time for that today. I'll try to do that in the morning.
Sorry for not fully describing the topology. The router 2.5g LAN port is normally plugged into a Netgear multigig managed switch that creates the hub of my wired LAN network. My AP (another GT-AX6000), my desktop PC, and my NAS are also plugged into this. LAN speed tests were between the desktop PC and the NAS (2.5g network port).
WAN speed tests gave the same result (1 gbps) whether my PC was plugged into the switch or directly plugged into the router 2.5g LAN port.