Ubuntu’s popularity often makes it the default choice for new Linux users. But there are tons of other Linux operating systems that deserve your attention. As such, I’ve highlighted some Ubuntu alternatives so you can choose based on your needs and requirements—because conformity is boring.
Aur is explicitly stated to be unsupported on Manjaro. I don’t think you can hate on them for this
https://wiki.manjaro.org/index.php/Arch_User_Repository
They should probably have big warnings when you actually try to go install something, then, rather than as a note in their wiki that very very few people will read.