@jcesardasilva 

Hi, were you testing the speed from the main Deco X50?

If it was from the satellite Deco, its speed will be 60-70% of the main Deco if they are connected wirelessly.

If it is from the main Deco, please turn off 2.4ghz and test the speed on 5ghz only. It is also suggested that you could have a test of the Ethernet speed from the main X50.

Since Deco X50 is WiFi 6, up to 2402m/s on 5ghz, please also check the link speed on your mobile devices:https://www.tp-link.com/en/support/faq/2265/

Another suggestion would be to set up QOS on Deco X50 to be 1000m/s download and upload.

  @Heidi_Alp 

Thank you very much for your reply. I've tried many things and all manipulations were done close to the main Deco, not on the satelites. I played with beamforming, fast roaming, QoS, different frequency channels, but nothing worked. 

Finally, I find out, with the help from the technical service of TP-Link, that the value 866Mbt/s as Link speed between my computer and the deco X50 is completely normal (unfortunately) since the deco is MU-MIMO 2X2, i.e., it has only 2 antennas 

My laptop has three antennas and can benefit from 3x3 MIMO, but the 2 antennas of the Deco is the bottleneck. The value 1300Mbt/s on the 802.11AC standard of my router confirms that my router is 3X3 MIMO.

The maximum value that the Deco reaches on the 802.11AC standard is 867Mbt/s. Deco X50 can reach up to 5 GHz: 2402 Mbps (802.11ax, HE160) 2.4 GHz: 574 Mbps. 

So, one can only benefit from a real gigabit connection with Deco if one has a brand-new computer/modern computer that supports MU-MIMO. To give an idea, for Apple's computer, only these can handle this today: 

Mac MacBook Air M1 (2020)

MacBook Pro 13" M1 (2020)

MacBook Pro 14" (2021)

MacBook Pro 16" (2021)

iMac 24" M1 (2020)

Mac mini M1 (2020)

Mac Studio (2022)

Since mine is from 2019, I am unlucky.