for the client config I recommend using configured:
https://www.curseforge.com/minecraft/mc-mods/configured

a copy of the default values is attached, but one is automatically created when starting minecraft


for the server config, it can be edited manually in a simple text editor (e.g. notepad)
the possible modifications are straightforward, just true/false values.
the server config needs to be copied in a folder called "defaultconfigs"
	in the .minecraft path for a single player world
    and in the the folder of the jar for a server (the folder will be generated after running the jar once)
	