@berne Keep router TP-Link AXE5400 as is. Just turn off router's WiFi. No other changes required on router.

@alfie012 There are no configuration settings in X55 for Ethernet link speed. X55 comes with gigabit Ethernet ports. Try different Ethernet cable(s), and/or return Deco X55 to the seller.

@Smats Deco M5 has a set of quite nice features that you might lose if adding another Deco model. Do you use the following with your Deco mesh: 1. "Test Internet Speed" button in Deco app; 2. IoT...

@MartinBG 500Mbps sounds too low for WiFi6. I am getting such speeds on WiFi5. Try this, in that exact order: 1. Switch Deco mesh to Access Point mode: Switching a Deco to Access Point (AP) Mode 2....

@alfie012 Please double check. Perhaps, reboot a computer and check again. If you force adapter to gigabit speed, it will not show you 100Mbps link speed: it will either fail to establish the link or...

@alfie012 On your computer, open Realtek Ethernet Adapter properties, change "Speed & Duplex" from Auto to 1.0Gbps Full Duplex.