I've never used it but I know Manjaro is basically a more opinionated and easier to use Arch. If you want rolling debian isn't an option but something like OpenSUSE tumbleweed is.
But I really wonder what's supposed to be so much better in terms of privacy on Manjaro.
I've been on Debian unstable for years on multiple devices, without major issues.
Now I run Ubuntu LTS with gnu Guix for most userland software.
There's nothing you can do with any of the security-oriented distros that you can't do with any other distro, but the security-oriented ones can ease initial configuration and perhaps make it less likely that you overlooked something.
Second, the defaults on something like Debian are very security focused. Out of the box it installs hardly anything.
Also I have never heard of Manjaro trying to be a "security-focused" distro until now. Not in the sense of OpenBSD, Whonix, or Hardened Gentoo. I'm sure it's not bad at privacy and security but really for most Linux distros this is a given.
But, again, that's a state you can achieve with every distro. It's just with normal distros, it takes more work.
Manjaro has little of this as a default out of the box. They are mostly able to claim that they are privacy oriented because any OS that isn't borderline spyware like Windows is privacy oriented in comparison.
There are various sandboxing tools but they are developed upstream, not by distros.
> as well as good security practices for the distro maintainers
Some large distributions do this, but it takes a lot of work. How many contributors does Manjaro have?