@Laserphile_007 

The easiest would be to set Deco mesh in Access Point mode. Even if you plan to get rid of TP-Link router, it'll be better to run Deco mesh in AP mode first, to ensure everything is working as you expect, WiFi coverage improved, etc. You will also become familiar with Deco configuration and management through Deco app.

There is very little that can go wrong when Deco mesh is configured in AP mode.

It is somewhat common misconception that in AP mode Deco mesh will extend router WiFi network. In both Router and AP mode Deco mesh will run its own WiFi network. That is why it is recommended to disable WiFi on router after deploying Deco mesh. Otherwise, you will have two separate independent networks at your place: from router and from Deco mesh, potentially interfering with each other.