SpectorJS is your friend … you can capture the frame and inspect what is going on, including shaders.
You will most likely find that all shaders on opaque meshes output 1 in alpha channel … or maybe all 0, not sure, capture frame and look at the shader.
You need to modify shaders so that meshes you want bloomed output 1, and others output 0 (or grayscale depending on level of bloom).
At the moment bloom shader converts pixel into greyscale and if it’s brighter than some value it blooms it. You would instead read that alpha value from the texture to decide if it should bloom.