@Manuel78 

With Deco mesh, Satellite Deco prefers to connect to Main Deco. It would only connect to another Satellite if signal from Main Deco is extremely weak or non-existent. Until recently, that was an automatic process with no user configuration option. TP-Link works on fixing it with new firmware, but it is not available yet for every Deco model.

If you happened to have M4 with version of hardware V4, you could try installing beta firmware on Satellite 2 and that firmware will unlock the ability to configure Satellite 2 connect to Satellite 1. You can find that firmware here: https://community.tp-link.com/en/home/forum/topic/581554

You only need to install that firmware on Satellite 2.

Configuration Guide can be found here: How to select a preferred signal source on the Deco App

  @Alexandre. 

Thank you for the quick and clear reply.

I have version V4 idd, so I'll try to update the 2nd module to the beta version.

Thanks

  @Alexandre. 

Hi

I was able to upgrade the firmware and I now have the required option.

Unfortunately when I try to save the change it fails to save..

I have tried to re-install the slaves, but still the same.

Am I doing something wrong?

  @Manuel78 

This is beta code, so it is most likely an issue on TP-Link side. Their Support scans forum topics, but just in case please also post about this in the forum topic about M4 firmware: https://community.tp-link.com/en/home/forum/topic/581554

Make sure you mention that your Deco mesh is M4(V4) only, with no other types of Deco models.

  @Manuel78 

As a follow up comment: someone reported that just by upgrading M4 to beta code it now connects to their Satellite instead of Main. Perhaps, that firmware had better understanding and management of weak link between Satellite and Main. You can try that: power off all three Deco, power on Main, then 1st Satellite and then after these both are up and online in Deco app - 2nd Satellite.

It is also possible if you could manage to move Main and 2nd Satellite a bit further away from each other, that will force 2nd Satellite connect to 1st now that it has firmware more willing to do that.

Still, please report that Deco is unable to save configuration, in forum topic I provided link to.

  @Alexandre. 

It is working now...

Thank you for all your help.

The saving issue was because not all modules where updated to the beta firmware.

After updating also the main module (already had done the other 2) I was able to change the link and save the setting....

  @Manuel78 

Thanks. I'll keep that in mind next time I recommend someone beta firmware for M4(V4). I was under impression only Satellite must be upgraded with beta firmware that needs to be configured where to connect.

That would explain issue with another M4 user who had three older M4, added M4(V4) and couldn't save configuration no matter what. Can't update his older M4s with beta firmware either.

In case you'll ever need to expand your Deco mesh, to avoid losing that feature, as of today (Jan. 2023) I would recommend you'll limit additions to your Deco mesh by M4(V4) and M5.

All hardware versions of Deco M5 got that firmware. For M5 it is release code, not beta.