I did run my Deco M9 in router mode and put in access point, but still had problems with Sonos.
I also run Eero now and I would strongly recommend running the Hub 3 in Modem mode and link the bottom port on your hub into the Eero / Eero pro.
On the other port on your Eero I have put a £20 8 way netgear gigabit switch which is working seamlessly and gives me more port options.
Yes you can run the Eero with your hub in Router mode, but Eero strongly recommend you don't and I have found when I have done this - yes it does let you use the ports on the back, but even if turning wifi off there is conflict with systems such as Sonos, amazon Echo systems being intermittent.
100% use on modem mode, Eero is a great system, not as powerful as some of the other mesh systems on the market, but one of the most stable I have ever used.