You can adapt the PKGBUILD below for use with KaOS. Double check the depends, remove the i686 arch and remove the pkgver() function. Build with makepkg -s. Install with pacman -U nameOfPackage.
https://aur.archlinux.org/cgit/aur.git/plain/PKGBUILD?h=rawtherapee-git
Example
pkgname=rawtherapee
pkgver=5.0.90
_commit=bc3003bc0dcdf60fc272c83ee204b5dc78ebe09b
pkgrel=1
pkgdesc="A powerful cross-platform raw image processing program"
arch=('x86_64')
url="http://www.rawtherapee.com/"
license=('GPL3')
depends=('fftw' 'gtk3' 'glibmm' 'gtkmm3' 'lcms2' 'libcanberra' 'libiptcdata' 'desktop-file-utils' 'hicolor-icon-theme')
makedepends=('cmake')
source=('rawtherapee.zip::https://github.com/Beep6581/RawTherapee/archive/${_commit}.zip')
md5sums=('SKIP')
You'll probably have to create a package for libiptcdata and gtkmm3 since they don't seem to be available in the repo.