As far as I know, CasaOS (same as Cockpit) is installed on top of a default OS install, so you could always access the OS directly to install/configure things outside of it, if the need arises.

I would not say you would be held back by it, if it does what you need. And for what I can see online, you can install any docker container even if it’s not on the default catalog of CasaOS, or access the OS.

If you want to grow your knowledge of how things work, or how to deploy services without CasaOS, you can always do so in parallel of using CasaOS, so I don’t see where the issue could be.

What would you recommend that is not NixOS or a Bash script and can be used agnostic of distro?

I’m going to mention Ansible as I haven’t seen it mentioned, and it can be used to locally manage a reproducible build.

It has already been mentioned, but as a minimum to replicate your system you need two things:

• Transfer/copy your entire /home directory as there is where the majority of the configuration files of your system pertaining the software you use (there could be configs you could need on /etc and on /usr/local or other dir), that is why it is recommended to partition your disk on installation of your distro, so the /home directory is already separated, as if you reinstall in the same machine you don’t lose any configuration in addition to your personal documents/pictures/etc
• Have a way to automatically install a list of programs/apps/drivers/libraries, and that is what something like a bash script, Ansible, nixOs, etc. could help you with.

The truth is that using any of the tools in the second point requires learning a bunch, so if your skill level is still not there, there is some work to do to get there.