Install Fabric Loader for your Minecraft version in TLauncher
Launch the game once with Fabric to create the required folders
Download and install Iris Shaders for Fabric
Place the Iris installer or mod file into the Minecraft mods folder
Open TLauncher and select the Fabric profile
Start the game
Open the Minecraft video settings
Open the shader packs menu
Download a shader pack in .zip format
Move the shader pack zip file into the shaderpacks folder
Select the shader pack from the in-game shader menu
Apply the shader pack and return to the game
If shaders do not appear, make sure Sodium and Iris are installed correctly
If needed, update your graphics drivers and restart the game