@Alpaslan 

This forum post from TP-Link Support will explain: The models that support "Test Internet Speed"

  @Alpaslan 

One more thing: for Speed Test to appear in Deco app you only need Main Deco to support it. If one of your Deco units supports Speed Test, promote it to Main Deco and you'll have that feature. How to replace the main Deco with another Deco

  @Alpaslan I have 2 deco X20 in my environment and one of them is main. So normally I need to see test internet speed on Deco App

  @Alexandre. 

Any other opinions?

  @Alpaslan 

If you want Speed Test from Deco, the only option is to get Deco unit from the list of models supporting this feature, add it to your Deco mesh and make it Main Deco.

  @Alexandre. 

My main deco is X20. It has a speed test feature but I cannot see in deco app.

  @Alpaslan 

Yes, this part is confusing with TP-Link Deco mesh: not only you must have correct Deco model, but it must be of correct hardware to support specific feature.

From link I gave you, it must be Deco X20 hardware V1/V1.2. Yours, according to what you listed, is X20 hardware V2. Hardware V2 feature set is different from hardware V1.