Hi Matt,
Due to nature of 5G rollout in the UK currently, it doesn't show as a network when manually searching.
The 5G 'should' connect when your device is connected to a 4G mast with 5G enabled as it used 4G as an anchor to connect with 5G.
Please note that while in 5G coverage area, it is possible that the mast your device connects to isn't 5G enabled and currently won't connect with 5G until the 4G connection is lined up with a 5G enabled mast.
If I've helped let me know 🙂
10 year's managing 9 Virgin Media accounts, and things never got any better, closed last 4 accounts since January 2021 :L
I give 'my' experience to help where possible.