Hi. Does "single Connect"" mean you have no other Connects or that your system consists of a single Connect (or rather  used to consist)? Are you resetting up a system or adding the Connect to a system that already exists?

S1 or S2?

The order in which you may have done things, might ‘possibly’ be your issue here. You mention you reset the Sonos App, reinstalled it and then performed a factory reset of the Connect, which presumably was using a wired ‘SonosNet’ connection, so it might be the case you connected the App back to the ‘existing’ Sonos Household, whereas if it’s your one and only device you will need to create a brand new Sonos HH and not use the existing one.

My thoughts are to try this (assuming it’s your one and only Sonos product) factory reset the Connect and also then reset the mobile Sonos controller App … On opening accept the T&C’s and first create a new Sonos System/HH to which you then add your reset Connect that will have a flashing green statue LED and continue on from there.

Note too that your mobile Sonos controller device must meet the system requirements mentioned here…

https://support.sonos.com/en-us/article/sonos-app-requirements

The WiFi network should ideally be 802.11b/g/n compatible (2.4Ghz band) and use security mode WPA2 Personal.

If problems persist, then perhaps try wiring the Connect to the LAN.

Only do the above though if the previously reset Connect is your one and only Sonos product.

Thank you for the responses.

I hope the following text answer the questions:

My system is a single Sonos Connect Gen 2 running S2-generation software. After wiping everything to start fresh, I no longer have a functional system.

I launched the Sonos app to set up a new system. I followed the instructions and reached the step where the Connect's status LED flashes green. After pressing the button on the Connect as instructed, I received an error message saying it cannot connect.

I am using a Samsung S21 phone with the latest Android version.

The issue is that I cannot install the system either over a cabled LAN or via WiFi. No networks are identified, even after disabling all network security. I also tried manually entering the WiFi name and password, but it still won't connect. Additionally, I cannot find an option in the Sonos app to set up the system via the LAN connection.

It might be best/easier to perhaps speak with Sonos Customer Support direct - I recommend you give them a call. Here is a link to contact the Staff…

https://support.sonos.com/s/contact

I suspect that the Connect software  is just too old for a user to  be able to create a new system. You should call Sonos Support - they can normally force through things that we cannot, and get it set up.

I am using an old UNIFI AP Long Range b/g/n certified for the WIFI.

Yes, You are probably right. I will call the support. 

You implied you have tried doing the setup with the Connect wired?

I ‘think’ you may have to enable ‘multicast discovery’ on your unifi WiFi device too - have you explored that, as mentioned on the manufacturers website? I mention it based on what I just read here at the below link:

https://help.ui.com/hc/en-us/articles/18930473041047-Best-Practices-for-Sonos-Devices