Thank you all who replied. Tow issues were at the heart of my problem: a test Ubuntu server with the same name, and the nginx service was not started.
# added this while troubleshooting and decided to keep it:
setsebool -P httpd_can_network_connect 1
mkdir -p /etc/ssl/private
openssl req -x509 -nodes -days 365 -newkey rsa:2048 \
-keyout /etc/ssl/private/netbox.key \
-out /etc/ssl/certs/netbox.crt
dnf install nginx
cp /opt/netbox/contrib/nginx.conf /etc/nginx/conf.d/netbox.conf
vi /etc/nginx/conf.d/netbox.conf
vi /etc/nginx/nginx.conf
# comment out server section
systemctl start nginx
systemctl enable nginx
cd /opt/netbox
cp contrib/gunicorn.py /opt/netbox/gunicorn.py
cp contrib/*.service /etc/systemd/system/
systemctl daemon-reload
systemctl start netbox netbox-rq
systemctl enable netbox netbox-rq
# verify:
systemctl status nginx
systemctl status netbox
The Apache install worked well too. Replace the nginx steps with these: