@Spike666 It is definitely a defective unit. Especially if you do see it reports in Deco app that it connects to the rest of Deco mesh on 2.4 GHz only.

@Marios_X It is possible to use Ethernet to have wired link between Deco units. You will not need to configure each Deco as different network for that. Start with this document: General questions...

@Tantalum Is it possible Internet is down at your place? If not, this is as far as I can assist. You may wish to contact TP-Link Support, now that you simplified your setup they may be able to assist.

@Senna7004 That would work, but I would suggest connecting both wireless M9 Plus to wired M9 Plus, if distance between them is acceptable. If not, you can just leave them as is. You can configure how...

@NoviceNoddy Main Deco M5 is capable of delivering up to 500Mbps speeds over WiFi, in tests I did with mine (I have gigabit Internet and could run M5 to its max). If they gave you a router and you...

@calmgate Any Deco model with Ethernet port can use TP-Link powerline adapters. I googled FRITZ!REPEATER 3000 and it says it is WiFi6 capable. If you want replacement to similar Deco, I suggest...