Did you “bond” the Sub4 to a soundbar?  If so what soundbar is the Sub4 “bonded” with?  Can you show a screenshot of the Sonos Room that the Sub4 is in?

Yes it was linked to an Arc Ultra . Two shots below of the different screens

Moderator edit: removed serial numbers from picture

 If the Sub4 & 300s are “bonded” the Sonos Room should look like this:  I don’t think the Sub shows as a room.  See if it can be added to the Arc Ultra room.  In your Living Room Arc Ultra Add a Sub should be there.

In your 2nd screenshot, if you click on Living Room, does the Sub show there?

Your Eras have not been added correctly as surrounds to the Arc Ultra. You have them grouped.

Adjusted set up, does this look right? 

When the rear speakers weren't grouped before I could adjust them separately and it felt like I was getting better surround sound. Doesn't feel like I do have good surround now.

Is there anyway of telling whether the Sub is working, probably linked to the above re being able to adjust individual elements of each device. 

All products are in the same room so yes that’s the correct Home Theatre configuration.

Before, your surrounds were outputting the same audio as the Arc Ultra, with a slight delay. There was no channel separation.

If you watch a movie, you will experience the surround sound as intended.

If the surrounds are too quiet, you can increase their volume under Surround Audio settings in the app.

With regards to the Sub, place your ear next to it to hear. You can also increase the Sub audio in the app too.

Thanks