I have found "xxx photos on this Mac only" by the suggested method - now what

I'm syncing Photos to iCloud from photos on my MacBook and used the suggestion of creating a new Smart Album to identify those photos.

Now what?

Do they just stay "on this Mac only"? Do I need to do something to get them synced to iCloud, and if so, what? I hope the solution is elegant because manually fixing 1,101 photos doesn't sound like a good use of my time.

And just out of curiosity because I like to know the reasons why (so maybe next time I won't do whatever it is I did to cause this), how does this happen?

Thanks.

MacBook Pro running Sequoia 15.0.1

Photos 10.0