With a single TP-Link Deco M4 AC1200 device, Wi-Fi coverage can be up to about 260 square metres (about 2800 square feet), but a distance of 20 metres to an outdoor cottage may be at or beyond the optimal range, especially if there are obstacles such as walls or environmental interference. The Deco M4 supports mesh technology, which allows coverage to be extended by adding additional units to ensure a stable and fast signal in distant or separated areas.

Therefore, to feed a PC, TV and other devices via Wi-Fi in a house about 20 metres away from the Fastweb Nexxt modem, a single Deco M4 may not guarantee optimal coverage and speed. It would be advisable to use at least two Deco M4 units to create a mesh network that effectively extends the Wi-Fi signal to the cottage, improving stability and connection quality.

Thanks, so I should cable one m4 to the modem and place the other m4 at m. 20.
Do you think this will work?
Thanks