Not sure what to call this, a hybrid HO palette image (HOO?)
I started off with a fully processed image(PixInsight) made up of 169 images captured thru a city light pollution filter and 121 images captured thru an Optolong L-eXtreme filter. The L-eXtreme images were longer so the total exposure was about 50/50 for broadband and narrowband.

Then I did this with PixInsight - The real trick is how you make the range mask !!

1. Split R,G,B (split channels RGB icon or with ChannelExtraction Process)
2. Rename R = Ha
3. Oiii has green and blue, so -
PixelMath: RGB/K - Blue*0.3 + Green*0.7 (check 'Use Single RGB/K..)
check 'Create new image', and 'Color space' = Same as target (ie greyscale)
Apply - we get a new image (grey)
Rename it - Oiii
4. Stretch both Ha and Oiii if they need it so both are similar
HistogramTransformation to bring up RGB/K - don't clip the blacks
5. Create a Range Mask for Oiii image
Create a mask - RangeSelection - we want mask to show bright and semi bright regions
Create a Real-Time Preview of Oiii
RMA - Lower Limit: 0.16 to show only most vibrant areas as white. Rosette:0.34 or 0.44
Upper Limit: 1.0 Rosette: 0.78
Fuzziness: 0.70 Rosette: 0.72
Smoothness: 65 to 70%
Another Try: Lower:0.53, Upper:0.76 - This worked well for Rosette Nebula !!
Click Apply to create range_mask and apply the new mask to the main Oiii image.
Background should red.
6. Stretch Oiii
range_mask on Oiii and bkgd red
Real-Time Preview
HistogramTransformation and stretch the data - don't burn out white
I brought center tab to 1/8 (was 1/4)
Apply and remove the mask
We now have Ha and Oiii data images !!
7. HistogramTransformation
Edit Ha with RGB/K so background looks similar to Oiii
8. Color combine with PixelMath
Remove Mask
UnCheck 'Use single RGB/K expression', Create new image, 'Color Space' = RGB
R/K: Ha
G: Ha*0.5 + Oiii*0.5 (Rosette Nebula: G: Ha*0.4 + Oiii*0.6 OK too)
B:Oiii
Apply - Created new image - didn't seem to matter if range_mask still on(protect bkgnd)
9. CurvesTransformation - on new image
Put on range_mask with background red
Real-Time Preview
Saturation - bring it up 1/4 area
Blue - lock 1/2 and bring 1/4 down
Green - 1/2 down slightly and bring 1/4 down
Red - decrease 1/2 - brought it down one line and blue popped out
Apply - Got a good effect by applying twice
10. Convolution to blur image - may want to put on a star mask to protect stars if too blurred
I had previously reduced the stars and the edges were to hard so blurring edges helped.
StdDev: more noise=higher StdDev - Highter noise: 4.00
Low noise Rosette Nebula: 1.5 StdDev and 2.0 Shape or stars got bad
Low noise Rosette Nebula: 2.4 for both was pretty good
11. LRGCombination ( mask on or off ??)
Range mask on (with red bkgnd) - added detail and contrast to blue with no effect on corners
Range mask off (with red bkgnd) - added detail and contrast to blue but lost faint nebulosity
Check 'L' and select Ha image
Lightness: 0.5
Saturation: 0.5
Can check 'Chrominance Noise Reduction' if needed.
Apply - really brings out the darker area - should see sharpness improvement
12. Rosette Nebula - put range mask on with background NOT red(ie invert the mask)
This will improve the fainter nebulosity in the edges and corners of Rosette Nebula
CurvesTransformation
Saturation - 1/2 up one line
Red - 1/2 up 1/2 line
RGB/K - 1/8 down a little, 3/4 up about 1/3 line
Apply

I learned a lot of this from this video -
RockyMountainAstro - https://www.youtube.com/watch?v=5M3zB7-Llhw&t=293s