A lot of mods say to find customization options in config.json, but I open all the files in the folders and find nothing that matches the config options. I have "show hidden files" turned on. I don't understand.
You will need to start the game with SMAPI once, when you hit the title screen you can quit, and the config.json files will have appeared next to the mods dll files.
huh Yes, I am using SMAPI. There's no second window. But... when I tried the Steam config instructions at the wiki, (https://stardewvalleywiki.com/Modding:Installing_SMAPI_on_Windows) the game didn't run, so I changed the launch address to C:\Program Files (x86)\Steam\steamapps\common\Stardew Valley\StardewModdingAPI.exe