This node setup seems unrelated to the discussion of how to recreate bloom in Blender 4.2, and it seems more like feedback about the veiwport compositor as a whole. Feedback about the viewport compositor is better suited on the viewport compositor thread: Real-time Compositor: Feedback and discussion
Unless you’re referring to the fact that in Blender 4.1 you would have this compositor node setup for final renders, and you would have bloom enabled in in render settings, meaning it’s visible in both viewport and final renders. But now that the bloom has been shifted to the compositor, you can’t use your complex final render node setups and your viewport bloom at the same time without a bunch of manual work switching between “viewport” and “final render” setups, or a add-on to automate that for you.
The most likely reason that node setup is failing is because at the moment the viewport compositor doesn’t support passes. Work is being done to add support here, but it’ll be in Blender 4.3 at the earliest.
After that, the most likely cause for that setup failing would be the use of multiple scenes, which I’m not sure if work is being done on.