@Aridus. I think there's some basic confusion in that forum. Ports 80 and 443 will always be open for 'outgoing' - IOW your PC connecting from inside your network to the outside world, eg when yu surf the internet. What is always blocked is 'incoming' which stops anyone from the outside establishing a new connection into your network. In router terms these are called 'egress' and 'ingress'. When yu type say bbc.co.uk in your browser your router goes out thru port 80 and establishes what is called a 'state' with bbc.co.uk - this state enables bbc.co.uk to send data back to you. However because ingress is blocked bbc.co.uk cannot start the conversation and establish a state.
You need to search on what is called 'port forwarding' whereby yu setup your router (your BT Home Hub) to:
a) open port 443 for incoming (ingress) so that any attempt to connect from the outside world on TCP port 443 to your IP address, or DNS registered domain, will be allowed in.
b) tell the router to forward that traffic to the internal IP of your nextcloud box - something like 192.168.x.x
This would allow say your smartphone contacts app to establish a connection state to your Nextcloud box and sync contacts for example.
This poses security risks however because anyone can type aridus.co.uk into their browser and they will be presented with your nextcloud login screen. Make damn sure yu setup the password from hell!! Like 4$G$7*NjADsJiX8s for example.
An alternative to opening ports on your home network, running a 24/7 server, and all the palava that this involves is to run your nextcloud on cloud VPS like digital ocean. They have automatic installs for nextcloud - you just click 'install me a next cloud server' (or sommat like that) and 2 mins later you have one - piss easy and only USD 5 per month.
Good luck...but be careful. There are very bad people out there constantly trying to get into your home network...