How does iCloud Photo sync process work when a new device (iPhone, iPad, etc) connect to iCloud sync?

One of my pet peeves about Apple and support articles, is that they say in order to get something to work, you just turn it on/off on each device. However, if Apple explained how certain processes worked, it would be much more helpful to understand possible issues and concerns that may arise in given situation.

Let's look at an example...

I have an iPhone 13 Pro and MBP M1 Pro Max. iCloud Photo sync on iPhone was NOT enabled (too many photos in iCloud already, and didn't need access on iPhone device). iCloud Photo sync on the MBP WAS enabled. I basically physically connected the iPhone to the MBP in order to IMPORT media in Photos on MBP which then sync'd to iCloud Photos (backup with full images, not optimized like on the MBP).

When things are set up this way, ALBUMS and FOLDERS on the iPhone do NOT sync to the MBP Photos... only the media comes across (you lose that meta data for the image, unfortunately). Of course, it becomes more of a challenge to re-create this organization on the iPhone onto the MBP over time (now).

Now that I have done this over several years, my iPhone storage (due to Photos, over 35,000) is reaching capacity and I want to delete Photos media on the iPhone (eg. keep only past 6 months of photos, for access, versus past 4 years). I don't want to enable iCloud Photo sync on iPhone as not needed, and can continue to sync with a physical cable, as needed.

My question is this... Is there a way (other than manually re-create, as painful) to get the folders and albums on the iPhone into iCloud Photos... and ultimately onto the MBP version?

I could temporarily turn ON iCloud Photos sync on the iPhone but what would happen... and then turn if off after it has completed, and then delete the localized iPhone media? Would larger iCloud photo store be an issue for iPhone that does not have enough storage?

Does the sync process "merge" photos/videos (no duplicates) from iPhone & MBP-iCloud versions, and does this also happen with folders & albums so that if one does not exist on one platform it is created, or if it does exist, it is merged? Or does the current iPhone-iCloud version "overwrite" the iPhone version, causing loss of folders, albums and possible media (eg if deleted on iPhone-iCloud version after iPhone sync).

Or is there another solution or approach?

Appreciate any help and feedback from someone who has tested this process before.

Thanks... Grant