@itsOmid With Deco mesh running in AP mode you can connect your file server to ISP router, which you have in front of Deco mesh. This is what I do at my home: my Synology NAS is hardwired to ISP...

@PWH I would recommend Deco X50 or X55. These two Deco models are similar in appearance and performance. They should have Connection Preference feature if you buy them new (from Amazon, etc.). If...

@Bigredm20 If your powerline adapters are compatible with Deco Ethernet backhaul, you can use them to link Deco in the summerhouse to Deco in the house and that will bring Deco mesh with powerline...

@MattS666 It is possible that Ethernet cable you are using is not recognized by Deco, or ISP router is not compatible with Deco Ethernet backhaul. You can test both: 1. Take Office Deco to the room...

@MattS666 For what you want to achieve, you need to switch Deco mesh to Access Point mode: Switching a Deco to Access Point (AP) Mode

@PWH Firmware 1.4.* does not have Connection Preference feature, it comes with 1.6. It is not guaranteed firmware 1.6 will be released for Deco S7. Powerline adapters are the last resort for wired...