I am loving your series. I did notice two things on this page regarding a Fedora install:

https://blog.kywa.io/mineops-part-1/

firewall-cmd --add-port=25565

should be

firewall-cmd --add-port=25565/tcp

otherise, you get an error no protocol is listed.

In addition, on the Fedora server I set up, I had to set SELinux to "permissive" or else I wasn't able to set the firewall OR get minecraft to work The command getenforce will tell you what mode you're in, and setenforce permissive will set permissive for THAT session, but will reset back to enabled on reboot.

If one wants to permanently fix it, you have to set both:

/etc/sysconfig/selinux

You need to set

SELINUX=permissive

or "disabled" if you like, and add it to the command line vua grubby:

grubby --update-kernel ALL --args selinux=0

This will remove SELinux on reboot. Security wise, not the wisest options, but the selinux portion of adding to Mine Ops is probably outside your tutorial's goals.