Also tried changing WPA type, disabling password, changing SSID, and literally everything.

Of course, also changing the positions of Decos multiple times, changing main Deco, hard resetting the decos, even buying the subscription (yes, 600 euro router requires subscription for Time Limit In parent control for example).

Also connecting Decos with cable, etc.

spend more than 30 hours trying all possible combinations, the devices keep disconnecting after 2-3 minutes and never connecting again.

*What an AI!*

Update for the users who follow the topic:

Since starting this topic I had multiple sessions with @TP-Link (thank you for that) for more than 12 hours combined.

Of course it is too annoying and time consuming to give access to them, to fix their own product every morning.

Today the remote session was 5 hours long and they managed somehow to connect some of the devices. It seems all of them are connected to the Main Deco, which is not good, because the signal is weak to the devices which are closer to the Satellite X90 and this makes once again the term "mesh" in their systems useless.

They said they will develop Beta for this case, but still I don't have it.

So just information for the new buyers, if you have some IoT devices or Homepod which you want to stereo pair, you will lose a lot of your nerves to make them work and you will not be able to do it.

If you want stable and good signal, you should take X90, you don't have a choise, however your IoT devices will not be compatible at this time with it.

Update: Today TP-Link wrote me that is not fixable issue.

Great! One more proof, this time for X90 it is useless peace of plastic.

  @Dave.W thank you for sharing that very much!

They are currently trying to "replace" my expensive X90 for X60 (which is 2 times cheaper), which is not solution in my opinion. And as now when you said this, I am not sure I will agree.

They said is because of the Broadcom chipset, but I am sure that they are unable to support their products, after this is the second high end Deco they can't deal it.

Maybe their developers are from India, just like Boeing.

So in my opinion don't go for X90. Just until they don't review all their practices and support, which in my opinion will never going to happen. They just don't care after they sold the product.
 

P.S. I shared my experience in the international Shelly group and it turns out many, many users are having this issue and are replacing Deco with competitions.

  @Dave.W Me too, I had more than 7 morning sessions, starting from engeneer who can't exit Vim and closing the terminal because of that going to the R&D.

They said that M9 problem is not fixable and 2 weeks later when I changed with X90, that the problem with X90 is also not fixable.

so based on your comment, I am going to refuse the offer (which is against me, based on the value anyway) about the X60. And if you want my advice - don't get X90. Out issues are some similar.

also they should add basic funcs like to choose the WiFi channel and I am sure the customers will tweak what is the reason why is not working.