Once the file is imported, you need to activate it in your world.
While Action Stuff is excellent, you might want to explore these 1.21-compatible alternatives (all working with Fix 55 equivalent updates): Once the file is imported, you need to
: Introduces fluid character movements, including first-person hand animations, new idle stances, and "crouch spamming". 3D Models & Items Once the file is imported
If the add-on is broken and you know how to edit files: including first-person hand animations
This guide aims to provide a general process. Specific steps may vary depending on the add-on and your device. If you're still having trouble, consider checking forums or the documentation provided by the add-on creator.