Reproduction steps:
1. Open the ‘IN-112577_STPAlphaProcessing' project
2. Open the ‘SampleScene’ scene
3. Select 'PC_RPAsset' asset in Settings folder
4. In the inspector window change the Upscaling Filter to 'Spatial-Temporal Post-Processing’
5. In the Post-processing section, enable Alpha Processing
5. Observe the Game view

Expected result: Cube is rendered through render texture
Actual result: Cube is not rendered through render texture

Reproducible with: 6000.0.56f1, 6000.2.2f1, 6000.3.0a6
Could not test with: 6000.0.0b15 (the feature did not exist)

Reproduced on: macOS Sequoia 15.6 (M1 Max)
Not reproduced on: No other environment tested