Most of that advice is a total waste of time.
Its new to me -its available for Slackware but i only came across when i started using Arch for some reasonI'm checking out Lynis from your link... fast, simple system auditing tool. I like it.
As @craigevil already said most of what is mentioned in that guide seems like waste of time. fail2ban I only run on systems running 247 so usually no not on desktops. As for changing the default ssh port, I only give access to my ssh port for specific ip addresses doing firewall whitelisting. Firejail sounds interesting and fun but seems to much like a PITA for daily use, although I have to admit I never tried it. Currently playing around with podman en containers on my homeserver and that is already a PITA because it's a different way of doing things.Yeah, some of it is okay. Some of it is really not that valuable. The stuff about SSH and jails, for example, aren't too bad.
Firejail sounds interesting and fun but seems to much like a PITA for daily use, although I have to admit I never tried it.