To cut to the chase, Flatpak is nice to have, but isn't a complete replacement, and the other suggested "replacement", Pacstall, targets Ubuntu instead of base Debian. If you want more detail, read the spoiler:
spoiler
I use EndeavourOS as my daily driver, so I'm used to the sheer convenience of the AUR. However, I'm not a fan of how that convenience is tied to a continually-changing rolling release distro. This becomes especially apparent whenever a major KDE update comes out, or the Arch Linux people decide to make yet another big change.
Debian is the other main distro I use. I mostly install it on systems I don't intend to use often, but recently I started dual-booting it on my main desktop. I like how slowly things change in the Debian world, and if it were easier to run uncommon software on it, I'd probably use it more.
I know Debian can use Flatpak, and while it is nice to have, it's not a complete replacement for the AUR. The other "replacement" MPR/Makedeb's developer suggested is Pacstall, but that's for Ubuntu and not base Debian. If Ubuntu were the same distro it were back when 20.04 came out, I wouldn't be opposed to using it, but Ubuntu's gone to shit since then.
EDIT: Inb4 Distrobox too.
EDIT2: The reason I want an AUR equivalent is convenience. Yes, I commit the cardinal sin of using an AUR helper when I use EndeavourOS. I like being able to install things and have them integrate into my normal system package management without having to manually set up scripts.
But I do; not everyone, but certain people. In example me as a certain people. I use the AUR since years and it has been great.
That's why its okay to use, if you know what you are doing and what you need.
Exactly. But then it is not integrated into the other packages (when we speak about AUR helpers), which includes handling dependencies and other stuff. Also it is much better to use scripts from others that are well tested and checked and updated. With the caveat that you don't trust everyone and will always check the script and sources before updating.
It's not always just
cmake. In fact there are many ways. Some even download pre-compiled binaries (from those sources you trust off course), others require custom work before making it work, with correct versioning and so on.I do not recommend that, unless it is very clear this could work. Because the dependencies are different. But with care and knowledge, as a starting point one could probably simply change scripts to make them work on Debian.