Is my understanding and typical observation correct that this sequence of actions will NOT create raw+jpg pairs? This is what I want as I don’t like raw+jpg pairs.
Yes, that is correct.
I recently followed this workflow for images from my Fujifilm X100V. The Apple raw engine doesn’t support the raws from that camera yet, hence I shouldn’t have imported those raws to Photos in the first place. But I apparently did. The interesting bit is that Photos suddenly showed raw+jpg pairs, indicated by the “J“ in the upper right corner. No error message from Photos. Then I wanted to edit a first image in Raw Power, and rightly so Raw Power gave me an error message.
Any idea of how that behaviour can be explained?
Well, if you imported the RAW+JPEG at the same time, then it makes sense because Photos uses the file extensions to decide when to pair things. However, if you imported the JPEG and RAW separately, then I would not expect that to happen. I just tried that myself and got two different items in the photos grid (I dragged a JPEG to the Photos icon and then I dragged the corresponding RAW [for a Fuji X100V]).
Photos will allow you to import unsupported images, and they should become supported automatically (you will want to quit and relaunch photos for that to work, I believe).