However is still the Luminar 3 unable to save edited images under Catalina , but this is not related to Apple rather Skylum who I understand is working on the problem.
I can currently not use any of the Skylum apps on Catalina, only with clumsy work-arounds.
To edit a. photo in Luminar 3 I have to open it in the full editor from the "Image > Edit with > Others" menu item. Once Luminar opens and I have finished editing the Photo, I have to use "File > Share > Open in Photos".
This will save an edited version in Photos and I have to deal with versions of the same image.
I hope the new Luminar 4, to be released on November 11, will fix this problem.