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I personally started out with Debian given that a vast majority of distributions are Debian based, typically paired with KDE Plasma 5 for my desktop environment, and learned from there.
Now Debian is really stable but does require command-line configuration quite often so it may feel complicated but if you’re capable of reading & following documentation then you should be all good.
Distributions like Ubuntu, Kali Linux, Linux Mint are actually based off of Debian however, each distribution provides their own packages and typically have system files in different places, so packages made for Ubuntu may or may not work with Debian and vice-versa.
KDE Plasma is a Desktop Environment (aka your desktop). When you install a Linux distro on your computer you’ll typically be given an option on which software you want to pre install. You’ll see software like GNOME, KDE Plasma, Xfce, Cinnamon, etc and by doing a little research into them you can pick the environment that suites you best.
GNOME gave me MacOS vibes while KDE is more Windows.
Hope this explains things easily!