Can anybody recommend a trustworthy guide to configuring the firewall in Ubuntu 23.04?

As far as I know, ufw (uncomplicated firewall) hasn't changed on 23.04, so this guide should still be good:

https://www.digitalocean.com/community/tutorials/how-to-set-up-a-firewall-with-ufw-on-ubuntu-22-04

This one mentions a GUI for ufw:

https://www.linuxcapable.com/how-to-install-and-configure-ufw-firewall-on-ubuntu-linux/