It seems to pick up my domain level email with my server, which is not what I use. I am a bit geeky, but this is very confusing tbh.

How about some details to work with. You want clues we need information.

Starting with what is the domain? Is it correctly configured in DNS to send and receive mail? Try your site in this website to see if it is all setup correctly. https://intodns.com/

I am more than a little confused by the statement "It seems to pick up my domain level email with my server, which is not what I use." you are going to have to go into some specifics I think. what exactly are you trying to set up The wizard makes some assumptions, but mostly it relies on DNS to detect the mail server. Having said that there is a manual configuration for just those occasions as when it assumes an incorrect server domain.

Thanks

I did manage to mess about with the server settings from this tutorial, and it worked - phew!

Adding the Google server settings worked for me - they do need to make it easier though tbh.

https://www.hostpapa.com/knowledgebase/add-gmail-account-to-thunderbird/