@N880ep 

Hi

If Hub 5 is in modem router mode, you could refer to the following link to change Deco to access point mode:
How to set up Deco to work in Access Point mode
If Hub 5 is in modem mode (like a bridge), you do not need to change the mode of Deco because the default mode of Deco is wireless router mode.
Both setups are viable options, so you might want to decide based on your speed test findings and the layout of your actual home.

  @N880ep 

Like you, I have just upgraded to Virgin 1gig fibre and received a Hub 5. Previously I had a Hub 3 in modem mode and my Deco S4s were in standard mode.

Everything worked very well.

However to get the best out of the Hub 5 I think you need to use it in router mode but turn off the wifi on the Hub 5 and switch the Decos to Access Mode,

this allows all ports on the back of the Hub 5 to be available for wired devices.

I find performance much improved in Access Mode.