@ruadauto19 

Hi, welcome to the community.

Take 2* Deco X68s and 1* Deco M5(all in EU version) for example, the 2 Deco X68 would still work as expected with 3 bands(2.4 GHz+ 5GHz-1 via UNII-1+5 GHz-2 via UNII-2C band) when they are wirelessly linked with each other. When a Deco M5 is wirelessly connected to Deco X68, the Wi-Fi Backhaul between M5 and Deco X68 would only always be 2.4 GHz and 5 GHz-1 (UNII-1) since M5 is only a dual-band Deco.

But I see you tend to connect Deco M5 via Ethernet cable to Deco X68, in that case, they would use Ethernet Backhaul directly, and no longer use Wi-Fi Backhaul.

But if the 2*Deco X68 is the US version, 5 GHz-2 of Deco X68 uses U-NII-3 which might not be allowed in some regions. So at this moment, even if you have two Deco X68s, the Wi-Fi Backahul between them is only 2.4 GHz and 5 GHz-1.

In this way, to guarantee optimal performance, it is always suggested to purchase products in the local market and retain the same EU or US version.

Thank you very much.

Best regards.