To Sync photos from this Mac turn OFF iCloud Photos?????

t is not possible to mix the old way of manually syncing your photos from a Mac to your iPhone with iCloud syncing. You will have to pick one horse and ride it.

Mixing manual syncing and iCloud Photos will be asking for trouble in several ways:

• If you previously have synced photos and videos from a computer to your iPhone or iPad, the manually synced items will be erased completely, when you enable iCloud Photos on the iPhone or iPad. If the synced photos are your only copies of these photos, save them, before your enable iCloud Photos.
• After turning on iCloud Photos on your iPhone or iPad, you should no longer try to download photos and videos directly from these devices, baut always use the iCloud syncing to transfer your photos ans videos. Only the items currently downloaded to the device will be visible when you try to download them. And the iCloud syncing is changing the file properties. The duplicate detection on import will no longer work reliably and you would be risking duplicates on import.
• You will no longer be able to sync selected items to the iPhone or iPad. iCloud syncing is all or nothing.

Switching from manual syncing to iCloud Photos is a very good idea. But you should plan it in advance. As your complete Photos Library will be uploaded to iCloud, you may want to split your Photos Library:

Only the System Photos Library can be set up to sync with iCloud. All other Photos Libraries will remain local. When I set up iCloud Photos, I copied my current Photos Libraries to an external drive to archive them. Then I weeded out my System Photos Library, to make it suitable for syncing.

The iCloud Photos Library on your Mac is now holding only these items:

• All photos and videos that I am currently working on to add adjustments and titles. keywords, etc.
• All my Photos that I need for my current projects.
• All my favorite photos, that I want to have accessible on all devices at all times and that are so important to me, that I want to have them stored offsite, for an additional safe keeping.

And all my photos are stored on an external drive in separate photos libraries, and this archive drive is occasionally copied to a backup drive.

You will also need to make backups of your system photos library, that is syncing with iCloud Photos. If you decide to use "Optimize Mac Storage" for your System Photos Library, it will be very hard to make backups. I do not use optimize Mac Storage for the Photos Library. I keep it small enough to fit on all devices without optimization. This way all photos are stored locally on all my Macs and the Time Machine backup is saving my system photos library. If you want to use "Optimize Mac Storage" you could use this method to get a backup of your system Photos Library: How to back up an optimized iCloud Photos Library - Apple Community

There are currently two different ways to sync photos and videos from your Mac to your iPhone: the old way using Finder is one-way and rather clunky; the new way is via iCloud Photos. The two ways are incompatible at the phone end. I'm not sure where you were reading, but somebody wishing to use the Finder-sync method would have to turn off iCloud Photos on the phone.

You asked, "What do I need to do to just upload my Mac photos TO iCloud and then have than download to my other devices"?

The answer is you need to enable iCloud Photos on your Mac and on each of your other devices. Note that this will have the side effect of uploading any photos you take with your iPhone or iPad and downloading them to all other devices; all devices connected to the same iCloud Photos library will have the same collection of photos and videos to the extent possible.

You're welcome, flabbygum. 😊

You mentioned a "much bigger problem that is preventing any of my devices from syncing iCloud Photos". Could you solve this already?