Just wanted to loop back round and update this - my problem was that valet wasn’t listening to port 80. After doing this:
some stuff
Which I think culminated in
valet uninstall
rm -rf ~/.valet
composer global remove laravel/valet
composer global require laravel/valet
valet install
I got a pop up asking if Valet was allowed to listen to port 80, and then everything worked again.
Thanks again for your time @danielroe…