bloom will work if you use "PP_post-tonemap" or set the blendable location to "after tonemapping"
expect flickering if you do that though, i can't tell if this is because of a limitation with the rendering system or a limitation with my brain
I found a fix for the after-tonemapping flickering here:
https://github.com/DaveFace/UnrealRetroShaders#optional-step-1---disable-grain-q...
Hope this helps someone