Confirm the active profile
Launch your Fabric profile once and make sure it starts successfully before adding anything. If you have multiple game instances, find the game directory for this specific profile; changing another instance's mods folder will not change this one.
Add the matching file
Download the Fabric build listed for your Minecraft version from the official project. Read the file details for dependency requirements, then close the game and place the jar in that instance's mods folder. Keep the downloaded jar intact rather than extracting its contents.
Check the first launch
Start the same profile and review the launch log if anything fails. Note the Minecraft version, Fabric loader version and exact Clumps filename before making further changes. Once the world opens, visit a familiar XP collection area and compare a short session with your previous experience. Keep the full log if you need help diagnosing a failure.
Next step: read the installation guide or find a matching download.
Project reference: Official Clumps project and file details.