Thank you so much for responding!
I went to ‘What’s my IP.com’ which gave me one IP address, then on my mac I looked in System Preferences> Network > Built-in Ethernet > Advanced > TCP/IP and this gave me a different IP address. I logged into my router and the info there matched the info on my mac, so I tried changing the fields in Home Assistant from Automatic to Static and entered the details I found on my mac there. I took a screenshot of the details I entered, but not of the original automatically populated fields…
From your response, it’s clear I have done this incorrectly! But now I don’t know how to get it back to its former state.
For the HACS install, I followed a video tutorial on youtube by a user named ChuckBuilds: here. It think it follows the guide you linked.
Thanks for your reassurance, I hope I can get it back up and running!
UPDATE: linking to this post which is similar.