How could I add more repos like Debian / Ubuntu?

Hi, i’m using on my other maschines ubuntu, LM, debian. Mostly with KDE.
so for now there are 2 questions for me.
The first is for my kids. My oldest son is using LM21 and it is quite wokring for him. I know that missing programms could be added by adding an other repo (or more repos); so for some missing apps i add a ppa or the program itself brings at installation a new repo within.
My younger twins should now start with manjaro-kde (especially with g-compris) because i think kde is quite comfortalbe to use, even if you start with “computing” .
But i think at some point in future there is maybe to few options for apps (for my kids) to play/work with so how could i add more repos in a “big” way like it is in debian/ubuntu? Are there some aur that contains more than “one or two” programms or is the method behind the aur that it is only some few programms in the aur?
If someone could give me some hints to that i would be thankfull.

This is not recommended on stable branch as it requires custom packages and therefore entirely unsupported. The same goes for third party repos - they are unsupported.

The custom script repo is Arch User Repository - and as the name implies - assumes Arch package level - which is only available when using unstable branch.

If you come to a point where this becomes important only 2 steps is required

  1. Switch to unstable branch and run a full system sync
    sudo pacman-mirrors -aS unstable && sudo pacman -Syyu
  2. Open the package manager and navigate to PreferencesThird Party tab and enable AUR.

NOTE: Do not enable neither update check options - this may cause issues when doing regular sync where packages has been removed from the repo. This removal is often done upstream from Arch - and in such case the packages is moved to AUR - which in turn causes sync issues.

The AUR is a whole, community-maintained repository for Arch packages. It can be used on Manjaro with some precautions.

Ah okay.
So are there than different AUR repos? one for arch itself and one AUR for manjaro?`Or could it be the same base?

There is only one AUR.
Manjaro can use it, but expect problems when you are on the Manjaro stable branch.
as that does not carry the same software versions as Arch does - which is expected for the AUR packages to work.

AUR is a book with build recipes - there is only one book - the recipes works for Arch - and usually they work for Manjaro - yet unsupported.

It contain information the makepkg process use to create an installable package.

This process may download a package designed for Debian - unpack it - and patch it for Arch and repack it OR the process downloads the source - patch it for Arch - compile and pack it.

Please refer to the above link to the Need To Know document.