You said arch is not for beginners, OP is asking for a distro to learn. I asked why atomic is not for beginners, not for someone to learn. Op also didn't say what she wants to learn about linux. Maybe she is no software dev and doesn't want to learn how to package software. But even then, distrobox is only a few clicks away. Learning how to tweak the system before learning about firewall and other stuff is beyond beginner level in my opinion.

None of that describes why a beginner would not want to use a immutable distro. It only describes why it is not a good idea if you want to learn how traditional linux distros work. Not all beginners want to learn or care about how linux works under the hood and immutable distros can be a good fit for them. They might not be right for OP, but you have not describe any reason why any beginner should avoid them.