What to try in a linux distro ?

It sounds as you want to evaluate different Linux Distributions.

DE/GUI is a good one, terminal commands is a bit useless since the vast majority of Linux systems use Bash as default.

This is what I would look into on a new distro:

UI - What DE or WM is it using, what is the default config like, and try to learn from that. How is the terminal prompt configured (the default Ubuntu and Debian prompts are terrible, I allways change them)

Package Manager - how does it work, what software is available?

Unique software - Does the distribution include some tools, applications or games I haven't heard about? If so, what do they do, and how do they work.

This gives me a feel for the distribution and how to use it.

Try in what way?

If you've no prior experience with Linux, I'd say just try using it. For the average computer user, the overall experience will be very similar to Windows or Mac.

Go easy on yourself, and don't try to do/learn everything all at once. Just use the system like you would any other. Once you're comfortable with the overall experience, you can then tackle more complex stuff if/when you feel the need.

Edit: Just wanted to add that Fedora, Linux Mint, and Ubuntu are all solid choices for beginners.

First and foremost, that my hardware peripherals work with it (wifi card, camera, bt stuff if you have it...) - if not (and hope you don't nor would be frustrated by it happens), that there's a way to make it work

As in part of a review process?

Things like:

• Software update process
• Installing software which isn't in a repository
• Seeing how the community is for support ?

things that differ between distros, because everyone thinks they can do it better than others: multimedia and sound, firewall config, service management, different init systems, switching default when multiple packages provide the same feature and are installed in parallel, config file migration during updates, making and installing your own custom kernel, selection of free games available.

It depends on your goals with linux.

If your goals are on devops, you may find a good idea learn about docker, ansible and other tools to make your life easier. If you're a home user, maybe it's a good idea try flatpaks, for example. And there is much more, but you need to define your goals.

“If you don't know where you want to go, then it doesn't matter which path you take.”
― Lewis Carroll, Alice in Wonderland

I just tried them to see if they worked, but I'm a casual.