Don Goldman tutorial
https://astrodonimaging.com/tutorials/
Scroll to number 9. He uses channel colourising and clipping masks.
yes, its a video, but fast and concise.
Ive used this method for years now, ive tried many other ways, this one is obvious and very adaptable, its so simple and obvious I dont know why anybody would use anything else.
on reflection ,mmm, you would need to separate out the Ha, OII,SII images 1st