EndeavourOS is a rolling distro. It doesn’t matter from which ISO you install it, if you keep it updated, it will be the same. It’s not like 'Buntu or Mint. The name “Artemis” applies only to the ISO image, not to the installed system (which doesn’t really have a version, it just keeps rolling).
The problem is what @fbodymechanic said (please mark his reply as the solution): pamac-all is an out-of-date package and the maintainer seems to have abandoned it, that’s why you can’t install it. It doesn’t matter which ISO release you’ve used to install EndeavourOS. If the maintainer updates it, or someone else takes over its maintenance, then you’ll be able to install it. Alternatively, you can download the PKGBUILD file (and the source code, if necessary) yourself and fix it so that it builds, if you know how, but since you’re asking this question here, I presume that’s not an option. Or you can use pamac-aur-git, if you really must…
But I would echo the advice: don’t use Pamac, it’s rubbish. It’s designed specifically for Manjaro, and even there it’s not very good.
Besides, EndeavourOS is a terminal centric distro:
Welcome to the forum!