Before you buy a WiFi adapter. Try to give high priority to the PC in the app of Deco M5 and try different configurations in QoS. The problem is likely to be solved.

I need it too.

I have an IMAC 27 2009 connected by Ethernet to Deco 2 and I have no problem. It's very strange. Is the IMAC up to date?

I have the same configuration and it works for me. Maybe the problem is switch, I bought a Netgear GS105GE and I worked perfectly.

It is possible to use an Ethernet socket in the Deco 5-2 to connect it to the Deco5-1 and on the other Ethernet jack connect a PC?

Kienzlenator wrote Yes! In fact that is how I have mine configured, and it works wonderfully. thank you very much. So I save myself buying a swich. I configure everything for wifi and then connect...