Locate and select your desired modpack on Modrinth.
Select the Versions tab and make note of the name of the modpack version you would like to get (For example, if you would like a modpack for the game version 1.19.2, and the modpack version 1.0.0 is listed for that version, then that's the version you would want to remember). There is no need to download the modpack from here.
Open MultiMC and select Add Instance.
Select Modrinth, search for your desired modpack, and select it.
Select the version you wanted from earlier and then select Ok. Once it's downloaded, you can start the game.
Open the Modrinth App and select the Browse page.
Locate and select your desired modpack.
Select the Versions tab and download the version you would like to install. Once the instance is created, you can start the game.
Locate and select your desired modpack on Modrinth.
[THIS SECTION IS A WORK IN PROGRESS]
Open CurseForge Launcher and select Create Custom Profile on the top right of the page. This should open a new menu.
Towards the top of the menu you should see "Or import a previously created profile." Click on import and locate the modpack you just downloaded from MediaFire. This should automatically create an instance within the CurseForge Launcher with your modpack. Once it's created, you can start the game.
Select the Versions/Files tab and make note of the name of the modpack version you would like to get (For example, if you would like a modpack for the game version 1.19.2, and the modpack version 1.0.0 is listed for that version, then that's the version you would want to remember). There is no need to download the modpack from here.
Open Prism Launcher and select Add Instance.
Select either Modrinth or Curseforge, search for your desired modpack, and select it.
Select the version you wanted from earlier and then select Ok. Once it's downloaded, you can start the game.
Java is required for both macOS and Linux to run the Fabric Installer.
Run the file. When the menu opens, select your desired Minecraft version (For example, 1.19.2). Ignore everything else and click Install.
Open the Minecraft Launcher and select Installations. Click on the 📂 icon for any version listed to open the .minecraft folder. We'll be back here later.
Locate and select your desired modpack on Modrinth.
[THIS SECTION IS A WORK IN PROGRESS]
You can now launch the Fabric instance you downloaded earlier in the Minecraft Launcher.
Any launcher not currently listed may not support modpacks, or you may have to look elsewhere for a modpack installation guide!