Fabric is a lightweight mod loader, much lighter and leaner to forge. More and more mods are moving from Forge to Fabric for those reasons. So let's see how to install it:

Note: I personally had a problem with the fabric not showing up in the launcher versions. This guide will solve that issue.

Step 1: Download and install fabric

Installing fabric is pretty easy, simply go on the download page

Then click on Universal/.JAR if you're on Linux or macOS, or click on Windows/.EXE if you're on Windows. Note you will need to have Java installed!

Then simply execute the launcher (either by running a command or double clicking on it)

java -jar ~/Downloads/fabric-installer-*.jar

Once that's done, click on Install (don't forget to check the Minecraft version is the one you want).

Step 2: Adding the Fabric API and the mods

Many mods require you to install the Fabric API mod. Simply download the Fabric API mod corresponding to your Minecraft version here

Move that file to ~/.minecraft/mods/ (on linux and macOS) or to %AppData%/.minecraft/mods/ (on Windows).

Then, add the fabric mod(s) for that version into that same directory. I personaly like Xaeros minimap and ReplayMod.

Step 3: Adding a new launcher entry

The "normal" usage is as such, open the launcher, check there is a "fabric" profile corresponding to the version you installed (if there's none, make sure the "Modded" box is ticked).

If you have it, great! But in my case, I already had fabric 1.16 installed, and I couldn't find fabric 1.17 in the version list. If you have that same problem, add the following to ~/.minecraft/launcher_profiles.json

"Fabric <minecraft version" : {
      "created" : "2021-07-02T13:06:18.358Z",
      "gameDir" : "<path to .minecraft, like /home/snowcode/.minecraft>",
      "icon" : "Furnace",
      "lastUsed" : "2021-07-02T16:22:50.562Z",
      "lastVersionId" : "fabric-loader-<fabric loader version>-<corresponding minecraft version>",
      "name" : "fabric",
      "type" : "custom"
},

For instance:

"Fabric 1.17" : {
      "created" : "2021-07-02T13:06:18.358Z",
      "gameDir" : "/home/snowcode/.minecraft/",
      "icon" : "Furnace",
      "lastUsed" : "2021-07-02T16:22:50.562Z",
      "lastVersionId" : "fabric-loader-0.11.6-1.17",
      "name" : "fabric",
      "type" : "custom"
},

Once you did that, restart the launcher. You should now have a new profile showing up, simply hit the PLAY button next to it. Have fun!

Conclusion

Here is my second tutorial on this glog. I hope it was useful to you!

Good night!