@VarunAhuja If firmware upgrade was susccessful for all three Deco units in your Deco mesh, Connection Preference feature should appear in Deco app. This FAQ describes how to use it: How to select a...

@MOHAMMEDKHATEM Sorry, missed that model. Deco S7 is good, too, it is similar to M4 in performance. If you want extra Ethernet port on Main Deco, S7 could be a better choice: it has three gigabit...

@Adex1 This switch should be OK. You will not need to make any changes in Deco app. No features will be lost. If Satellite P9 is wired to and can use the switch, you'll see the following in Deco app...

@MOHAMMEDKHATEM In your case, get Deco unit from one of the following models: M4, M5 or M9 Plus. Make it Main Deco, see How to replace the main Deco with another Deco

@Adex1 If you can connect the third Deco to the second with Ethernet cable, you will not need the switch: If you can't do that, you will need the switch: Not every switch is compatible with Deco...

@Networker49 Do your run your Deco mesh in Router mode or in Access Point mode? The mode setting should be under Advanced in Deco app.