1.15 -> 1.16.1 jumploader JSON (outdated, Jumploader 2.0+ has custom game versions built in!)

jumploader.json

{
  "downloadRequiredFiles": true,
  "forceFallbackStorage": false,
  "overrideInferredSide": false,
  "disableUI": false,
  "launch": {
    "mainClass": "net.fabricmc.loader.launch.knot.KnotClient"
  },
  "jars": {
    "minecraft": [
      {
        "gameVersion": "1.16.1",
        "downloadType": "client"
      }
    ],
    "maven": [
      {
        "mavenPath": "net.fabricmc:fabric-loader:0.8.8+build.202",
        "repoUrl": "https://maven.fabricmc.net/"
      },
      {
        "mavenPath": "net.fabricmc:intermediary:1.16.1",
        "repoUrl": "https://maven.fabricmc.net/"
      },
      {
        "mavenPath": "net.fabricmc:tiny-mappings-parser:0.2.2.14",
        "repoUrl": "https://maven.fabricmc.net/"
      },
      {
        "mavenPath": "net.fabricmc:sponge-mixin:0.8+build.18",
        "repoUrl": "https://maven.fabricmc.net/"
      },
      {
        "mavenPath": "net.fabricmc:tiny-remapper:0.2.2.64",
        "repoUrl": "https://maven.fabricmc.net/"
      },
      {
        "mavenPath": "net.fabricmc:fabric-loader-sat4j:2.3.5.4",
        "repoUrl": "https://maven.fabricmc.net/"
      },
      {
        "mavenPath": "com.google.jimfs:jimfs:1.1",
        "repoUrl": "https://maven.fabricmc.net/"
      },
      {
        "mavenPath": "org.ow2.asm:asm:8.0",
        "repoUrl": "https://maven.fabricmc.net/"
      },
      {
        "mavenPath": "org.ow2.asm:asm-analysis:8.0",
        "repoUrl": "https://maven.fabricmc.net/"
      },
      {
        "mavenPath": "org.ow2.asm:asm-commons:8.0",
        "repoUrl": "https://maven.fabricmc.net/"
      },
      {
        "mavenPath": "org.ow2.asm:asm-tree:8.0",
        "repoUrl": "https://maven.fabricmc.net/"
      },
      {
        "mavenPath": "org.ow2.asm:asm-util:8.0",
        "repoUrl": "https://maven.fabricmc.net/"
      },
      {
        "mavenPath": "com.ibm.icu:icu4j:66.1",
        "repoUrl": "https://libraries.minecraft.net/"
      },
      {
        "mavenPath": "com.mojang:datafixerupper:3.0.25",
        "repoUrl": "https://libraries.minecraft.net/"
      },
      {
        "mavenPath": "com.mojang:authlib:1.6.25",
        "repoUrl": "https://libraries.minecraft.net/"
      }
    ]
  },
  "autoconfig": {
    "enable": false,
    "handler": "fabric",
    "forceUpdate": false,
    "gameVersion": "1.16.1"
  }
}

The metadata I used to make this is from https://launchermeta.mojang.com/mc/game/version_manifest.json, although you won't need this for Jumploader 2.0.0 and newer, just change the game version in the config from current to the version you want to use.

That's nice