It depends on what you want to backup. If you only use the default global libraries for KiCad, there is no need to backup them. If you use your own custom library setup, then you probably already have them backed up somewhere and know how to work with them.
Some time ago I modified one of the .json files myself to greatly reduce the mills grids listings and added a 0.001mm grid, so these now show up in the grid selection box in the toolbar (each sub-program has it’s own table).
But the simplest thing is really to just zip up the whole configuration directory and add a date in ISO_8601 format. That way you can use diff tools later to what sort of changes happen over time and this helps with putting some things back, even if you don’t know what setting it was or in which file.
And of course, some people put everthing in GIT…
All files in that directory are different kinds of settings.
If you delete the whole directory (or rename it), then KiCad just thinks it it freshly installed and it’s run for the first time and re-creates that directory with factory defaults.