Ported back a few fixes from Isonzo:

- Detect if the native plugin is missing, in which case the upscaler won't be initialized.
- Use the transparency & composition mask as input for the reactive mask initially.

Packages/com.unity.postprocessing@3.2.2/PostProcessing/Runtime/Effects/Upscaling/PSSRUpscaler.cs

@@ -25,10 +25,20 @@ namespace UnityEngine.Rendering.PostProcessing
 
 		static PSSRUpscaler()
 		{
-			if (PSSRPlugin.InitPssr() < 0)
+			try
 			{
-				Debug.LogError("Failed to initialize PSSR plugin!");
+				if (PSSRPlugin.InitPssr() < 0)
+				{
+					Debug.LogError("Failed to initialize PSSR plugin!");
+					PluginInitialized = false;
+					return;
+				}
+			}
+			catch (DllNotFoundException)
+			{
+				Debug.LogError("PSSR plugin not found!");
 				PluginInitialized = false;
+				return;
 			}
 			
 			PluginInitialized = true;
@@ -125,7 +135,7 @@ namespace UnityEngine.Rendering.PostProcessing
 			// We need to provide copies of the previous depth and motion vector buffers anyway, so we can turn this otherwise wasteful copying into a benefit
 			PrepareInputs(cmd, context, config, _inputColor, _inputDepth[frameIndex], _inputMotionVectors[frameIndex]);
 
-			Texture reactiveMask = config.reactiveMask;
+			Texture reactiveMask = config.transparencyAndCompositionMask;
 			if (config.autoGenerateReactiveMask || config.autoGenerateTransparencyAndComposition)
 			{
 				reactiveMask = GenerateReactiveMask(cmd, context, config);