[Update: Solution] TP-Link MR6400: internet only works over Wifi, no wired internet connection? Some webpages and programs load, some do not? A solution!

I recently bought the TP-Link garbage router MR6400. Everything worked fine, as I only browsed the internet on my phone over Wifi. I then realized that my connected Philips Hue had no internet connection and a LAN-connected PC also did not get internet. I also yould not access the router (via 192.168.1.1) from a LAN device. The firmware (december 2020) says up to date,
version 1.1.0 0.9.1 v0001.0 Build 200511 Rel.43036n

The provided solution from TP-Link says: enter a new
DNS (8.8.8.8, 8.8.4.4) which actually changed nothing, as expected. 

Also the provided information that your IPv4 IP-Address must show 0.0.0.0 (see TP-Link page here) is garbage! I write this post and my IP is 192.168.1.1, so the same that I use to connect to the router.

The solution: plug off the router, plug in all LAN devices, take out the sim card, plug in the router, wait for 1 minute, then plug in the sim card after the boot procedure. Voila. My pC and my Hue get internet this way. I guess it's a firmware issue, but TP-Link acutally does nothing but publish nonsense workarounds that do not help.

Second problem: on my computer, some programs and webpages were getting internet access, some not (for example, steam shop works, steam download only sporadically, google.de does not work, two minutes afterwards it works,...).

The solution: disable IPv6 on your computer'
s network adapter. It seems this is too new for TP-Link. I didn't try disabling in in the router settings, as only manual network provider search would work in this case. What the hell are these guys at TP-Link doing? Selling garbage hardware in combination with garbage firmwares.

Please write a comment if it did / did not help you. Thanks :)