@TheJunior 

Hey

To be honest what you are trying to achieve isnt within the capability of most Home grade hardware, Deco included as these are designed for just one internet connection.   What you are seeing when you disconnect Port1 (Internet 1) and it goes red then switches to port 2.. this isnt failover as such, more just the Deco looking for a WAN connection and happening to try port 2.    There is a chance if port 1 was still connected but not 'online' this wouldnt work... it would just go red.

To properly merge or setup a fallover on these connections you could look at a Load Balancing Router, something like the ER605 at around £50 / $75US which will handle both connections for you.  You can then set the ER605 to either bond the connections into one faster connection, or set a primary secondary solution for failover.     Your deco would then plug into this and it wouldnt know what internet you are using, or care for that matter.

In terms of seperate WiFi...  again unless you split your deco into 2 seperate installs / networks then guest wifi may be your only option.    What are you trying to achieve, its a bit unclear...

  @Philbert Thanks for your reply.

As a final expectation, I was looking for a way to split internet bandwidth based on devices.It happened that I hired a second ISP and so, I was trying to find a solution for reaching out my expectations but using low investments to achieve it. If Deco device could offer two ISP ports and understand that you want different networks (Wifi) for that, it would be what I was looking for.

Considering just one ISP, I could use the guest network to split my devices connection, but somehow, I would like to give priority for my work related devices on Internet bandwidth usage. For the two ISPs situation, now, I understand that requires a complete separated set of Decos. 

At last but not least, I'm using just only one ISP plugged, and if internet goes down, I will plug my second ISP.

Thanks again.