Is Endeavour the same or an exact copy of ArchLinux?
Or is it just a facsimile, I ask because sometimes Arch’s instructions don’t match (sometimes) with Endeavour, maybe, sometimes they are similar instructions.
Don’t pay too much attention to me, I’m coming from a friend’s wake and I’ve got a philosophical streak.
Greetings and happy Sunday. 
PS: sorry for my English, I’m Spanish.
EndeavourOS is built on top of Arch. Some things won’t work because the default, Arch way isn’t the way EndeavourOS did it. Most instructions from the wiki will work, however. If you have doubts about something, however, the forums are the best place to ask for help.
Arch itself has a philosophy.
Here’s some Arch documentation that addresses this:
Arch principals:
Particualrly Section 1.5, Versatility:
Arch Linux is a general-purpose distribution. Upon installation, only a command-line environment is provided; rather than tearing out unneeded and unwanted packages, the user is offered the ability to build a custom system…
And Section 1.4, User centrality:
Whereas many GNU/Linux distributions attempt to be more user-friendly, Arch Linux has always been, and shall always remain user-centric. The distribution is intended to fill the needs of those contributing to it, rather than trying to appeal to as many users as possible. It is targeted at the proficient GNU/Linux user, or anyone with a do-it-yourself attitude who is willing to read the documentation, and solve their own problems.
(bold text added by me for emphasis of specific points)
Also:
Warning: Arch-based distributions are not supported by the Arch community or developers.
No qualms , and hope you you are remebering the good. Anyways back to topic if you really want an informed opinion try both, see what works for you. Whilst EOS uses the repos of Arch it does a lot to ease the install process.
I speak english and still struggle at times to write this well