The unfortunate answer is that "it depends". Making Unix look a certain way will depend more on your workflows and preferred tools than any one particular singular grand unified guide
Just about every post has links to the github pages of the stuff they used
Pick any popular colorscheme, like dracula or catppuccin, get some good wallpapers and make a screenshot with your most-used (or just favourite) applications. Keep it simple
Alas, gnome themes is not working 😔
I'll try again when I have slept
If you are using Gnome stay with that first. You can try gnome extensions and gtk themes, there are lots of possibilities. Many of the things that people post for other window managers will not work on Gnome.
Then know your command line well https://github.com/jlevy/the-art-of-command-line
Then try to automate things, such that e.g. you can open a QR code of your clipboard with a key binding. Or whatever cool things you want your computer to do.
If you like these things and you have a lot of time, try other window managers as well. Start with something that has a good example config and good resources online, I believe sway was pretty easy to get into for me.
$ man man
$ info
How? Installing the right tools and changing configuration files wich are typically (but not always) located under /home/[your user]/.config/[application]
For example neofetch config is located at ~/.config/neofetch/config But i think that's not the default config. An example config would be typically (but again not always) located at /usr/share/[application)
So what you would do is
cp -r /usr/share/neofetch ~/.config
vim ~/.config/neofetch/config
And edit the file however you want. Syntax is rarely the same between apps so prepare documentation if you do more than just change values
(Replace vim with you editor of choice)
The best starting point in my experience is https://regolith-desktop.com. You install it and get a noob-friendly, pre-configured unixporn desktop out of the box.
Once you start using it, the rest of the obscure programs referenced on /r/unixporn start making sense too.
Install hyprland and waybar, then check their wiki/docs
Submit screenshots of all your *NIX desktops, themes, and nifty configurations, or submit anything else that will make themers happy. Maybe a server running on an Amiga, or a Thinkpad signed by Bjarne Stroustrup? Show the world how pretty your computer can be!