NGC 3532, also commonly known as the Pincushion Cluster, Football Cluster, the Black Arrow Cluster and the Wishing Well Cluster, is an open cluster some 405 parsecs from Earth in the constellation Carina.
Distance: 1,321 ly (405 pc)
Constellation: Carina
Apparent magnitude (V): 3
Hopefully constructive thoughts: I think you've got excellent data there, but the processing is letting you down. Easily fixed.
The cluster stars are blue-white. That's good. But the background Milky Way stars are the same colour. They can't all be OB stars! Have a look at some of Mike Sidonio's wide-field shots where the Milky Way stars are, as they should be, quite orange, like golden sand.
Secondly, you've pushed the background (too much curves) too hard, so that the background is gritty/blotchy instead of near black, and the main cluster stars, instead of being sparkling gems, are bloated spheres.
You should not need to use any noise reduction at all on an image like this.
Actually that's not blotchy IMO there's a lot of background nebula in that region so I needed to apply aggressive curve to bring that out, the halo effect was applied by Starfilter Lite, attached is a little less aggressive image less halo effect
For what its worth, here's our Ha LRGB version: https://photos.smugmug.com/Category/...ach%204096.jpg. You are right about the nebulosity. Notice the large number of red giants in the cluster itself. They are just starting to become differentiated in your repro.