I don’t know a way how to get the old look back… as many others don’t know it currently as well. Epic did not give us a solution or how-to yet. There are various threads regaring that issue. The new tonemapper could look better in realistic szenes but turns around the emissive colorwheel way too quick and even on the bloom colorwheel which is less than before and even another color. Probably they did that to make the path ready for upcoming HDR monitors but actually it’s counter-productive for art that should be displayed on mainstream monitors and should not look like a photo. You would like orange emissive with orange bloom - and don’t give that much if this is physically correct in terms of a colortemperature of a black body? In a comic this is no issue… as well in any fantasy or sci-fi theme. With the new tonemapper you get white emissive with little yellow bloom instead. So you have to tinker around a lot and usually the most solutions affect the hole game. It’s more difficult with bloom as everything starts “bloom-bleeding” that way (if you increase bloom for example). Your issue seems a bit more like “tuning the color temp at a monitor”. Probably you could tinker a bit more with some different LUT textures (as I wrote I just tried a few seconds based on those two screenshots you posted) and get a better result if you try a bit longer. But I’m afraid there is no “make it like < 4.15 again” switch.
https://answers.unrealengine.com/questions/565285/howto-neon-light-material-with-new-tonemapper-in-4.html
https://answers.unrealengine.com/questions/581853/how-to-configure-bloom-in-415-to-look-like-in-4143.html