I can't add a new printer (several problems...)

Setup the printer using a static IP - this is usually done by using the printers physical control panel.

Another option to configure the ip address is the printers web interface. To locate the printer’s current IP address - probably DHCP assigned - you can use arp-scan.

sudo pacman -Syu arp-scan

Then

sudo arp-scan -l

You will see all devices on the network Open a web brrowser and point it to the IP address you think is your printer.

When that is in place - you can add the printer in cups webinterface ipp://v.x.y.z

Using DNS-SD requires the avahi daemon to be up and running

systemctl enable --now avahi-daemon.service avahi-dnsconfd.service avahi-daemon.socket