KDE, especially, is known for its amazing themes and theme customisations. With that can come lots of tweaking, and then forgetting how to get back to what you really liked. Or maybe you want to share that fantastic theme combination that you got right with friends.
Konsave helps do all of this very simply and effectively. I do like that all its options are logically named like -r for remove, -l for list, etc. So, although it is command line driven, it is really easy to use.
It officially supports KDE Plasma, but can be used on all other Linux desktop environments too. It is an open-source application written in Python.
See https://github.com/Prayag2/konsave
EDIT: SaveDesktop at https://github.com/vikdevelop/SaveDesktop. SaveDesktop is also worth looking at. It is a GUI alternative with a Flatpak installation.