plasma-manager VS dotfiles

Unfortunately until we find more volunteers in this area, it is hard to see status quo changing. See also https://github.com/nix-community/home-manager/issues/607 and this ongoing project https://github.com/pjones/plasma-manager

Plasma-manager solves both backup and sharing.

A dude wrote a tool to configure KDE with Nix. https://github.com/pjones/plasma-manager Sadly it's a bit iffy, and settings aren't applied until you relog and other things.

Normally yes with the help of home-manager, but you cannot manage your Plasma configuration declaratively, yet. I think there is an effort for configuring Plasma here, but it is not complete yet and did not get any updates since September so maybe it is abandoned or paused for now? If you are fine with using Gnome, there is a dconf module in home-manager so you can also make your desktop environment reproducible. There is also xfconf module for configuring XFCE if you prefer that but I did not use it so I don't know if it is as good as dconf.

however, there is the Plasma Manager which should give you similar or even the same experience as GNOME

Although I still have to look into plasma-manager

As for declarative usage for KDE or Firefox, while I haven't done it personally yet, it is possible by adding extra modules. Home-Manager has config options for Firefox and Plasma Manager, an home-manager module for KDE.

Think I'm going to start using plasma manager and maybe try to contribute.

I've been using plasma manager for kde, it has a command to dump the current configuration to a nix file which is convenient https://github.com/pjones/plasma-manager

On NixOS (probably irrelevant for you, but may as well mention it for others) I've been using plasma-manager.

Every option I want to have changed is in my vars yaml file. The change is made through the ini_file module (while also abusing include_tasks a lot to iterate over the config hash).