For example, the cloud where it says "Broadband backhaul", what does this refer to exactly
In the case of FTTC/FTTP it's the network between the OpenReach L2S and your ISP end point, which is almost always in London.
Many ISP's don't have their own backhaul and will use a Wholesale provider. The main 2 Wholesale backhaul providers are BT Wholesale and Talktalk Business.
BT Wholesale have their own fibre that criss crosses the UK. They provide the backhaul for hundreds of ISP's.
Talktalk don't actually own the majority (or maybe any) of the fibre they use for backhaul. It's made of mainly of dark fibre that they rent/lease from multiple networks.
Some providers use multiple backhaul providers. Some let you pick which 1 your line will use, others don't. Some will even let you change this mid-contract.
For example I could buy 2 lines from AAISP and have 1 line use BT Wholesale backhaul and the other use Talktalk Business backhaul.
Both lines connect to the exchange on the same OLT and L2S but they leave the exchange on different backhaul networks, taking different routes across the country.
Both would end up routing my traffic to AAISP.
Other large providers with their own backhaul network are Sky and Vodafone.
Sky don't Wholesale theirs like BT/Talktalk. I believe Vodafone do.
BRAS is done differently by different backhaul providers.