I've recently purchased a Deco M4 for my home WiFi solution. Before this, I had 3 pre-existing Deco E4s scattered across my house but quickly realised that I'd made a mistake by capping myself to FastEthernet speeds when I have a synchronous 200Mb/s Internet plan provided by my ISP. I've recently setup my network from scratch while setting up the M4 as the master router and all the other E4s as my satellites. This quickly solved my problems with my home's wireless speeds and I got my full bandwidth across the space. For context I've set them up in AP mode and not WR.

Now, the problem arose when I plugged in my Laptop to the master M4 in my room via a CAT6 cable. I've tested the cable and I've received the proper Gigabit link so that's not an issue. My Deco seems to only give me 100/100 when I look at the settings. I know my switch from my main router is working just fine, and is able to send the M4 a Gigabit link.