iPhone photos uploaded on iCloud - not appearing in photos mac when connecting iPhone via the cable iPhone 6S - IOS 13.3
MacBook pro - El Capitan.

I have enabled iCloud Photos on iPhone - with Optimize iPhone Storage.

On Mac, I haven't enabled iCloud Photos, as I don't wish to have all my local photos library being uploaded to iCloud. 

My ideal use case would be to have iPhone uploading photos to iCloud, as a first layer of getting the photos out of the iPhone, then periodically to connect my iPhone to my mac and import all the recent/not imported photos from it to my local mac library.

However, when I connect the iPhone via cable to my mac, Photos app can't find any new photos on it - although they exist there. 

So I am wondering if this is expected behavior and if there is a way to achieve my ideal use-case?

Also, isn't there an one-way of syncing, for example to have my Mac only getting/downloading images from iCloud, instead of doing both uploading and downloading?

Now that I am thinking of it, maybe the Optimize iPhone Storage might be preventing this, as the original images do not reside on the iPhone - however, shouldn't I be able to access/see those as not imported on my mac?

What would be the workflow, if I turn off the Storage Optimization? Would the iPhone upload the originals to iCloud and also keep them in its local drive? Would that allow me to connect it to my mac and import the photos?
You have three questions here and I'll try to answer them, as they are intertwined, but in general it is better to ask one question at a time:


  isn't there a one-way syncing? 


Sort of. There is Photo Stream which allows you to upload the iPhone's images from the last 30 days, which you can then import into your photos library. In your case, you'd have to enable iCloud Photos and My Photo Stream on the iPhone and only enable My Photo Stream on the mac. It would mean though, you have to import your photos/videos at least every 30 days to stay up to date. The support site is quite clear and even explains the differences.


  maybe the Optimize iPhone Storage might be preventing this


Yes. That is exactly whats happening. Only actually downloaded photos/videos will show up on your mac. You could (if its just a very little amount oh media you want to import) manually download them before connecting to the Mac and afterwards import them.


  What would be the workflow, if I turn off the Storage Optimization?


Turning off storage optimization would mean your iPhone would redownload all previous media and save them locally and also keep them on iCloud. Future photos/videos would be saved on iCloud and on your iPhone. This would allow you to import any media on your Mac. 

I hope this helps.