Photostream vs iCloud Photos / iMac library

That didn’t answer my question. I know how to transfer files.

So Photostream did that transfer automatically and in order to use iCloud Photos to do this, my photo library has to be stored on iCloud. So more precisely my question is: When iCloud fills up, e.g., 5 gb is used, will newly taken photos from my iPhone overwrite the oldest files in iCloud or will it just stop working and constantly remind me that I need to purchase more space?

My Nikon camera will continue to automatically sync to my Mac but I assume unless I buy space from Apple, my Apple devices won’t. So have we gone full circle, from “it just works” to “it’s only money”?

I probably have 200-300gb of photos in my library that I certainly don’t want to store in a cloud. So I will be forced to manually transfer photos to my library unless I pay for a subscription. I guess 166 billion dollars profit/year wasn’t enough for Apple.