Photos app favorites not syncing between iPhone and MacBook Pro

I'm not sure how you're dealing with Favorites. iCloud Photos synchronizes all pictures in the Library. Or are you using a USB cable to transfer pictures?

First, try a Forced reset on the iPhone:

Force restart iPhone - Apple Support

This is different from a simple Power Off. For me, the logo appears  5 or 10 seconds past the "slide to power off" message. Wait for the logo; don't do the slide thing. 

On the Mac,

• Restart the computer (of course)
• Re-start in Safe Mode. This bypasses certain potentially disruptive processes, and it often helps. Safe Mode is different for different computers, so see this: 

           Start up your Mac in safe mode - Apple Support 

Can you give us a bit more information?

1. What is your storage on this iPhone? At Settings>General>iPhone Storage, my phone says 50.5 GB of 128 GB used. What does yours say? 
2. At Settings>Battery, what do Battery Health, Maximum Capacity, and Cycle Count say?
3. What is your storage on this Mac? At System Settings>General> Storage, my Mac says 745 GB of 1TBB used. What does yours say?
4. On your Mac, do you have more than one Photos Library?
5. Where does your Mac's Photos Library reside-- in the Pictures folder of your internal drive, or on an external drive? or on a network? on iCloud drive?
6. Are you using iCloud Photos to synchronize your devices? If so…
7. …Do you have “Optimize Storage” checked in Photos’ Settings on the phone?
8. …Do you have “Optimize Storage” checked in Settings on the Mac?
9. …Do you see all your Mac’s  pictures at iCloud.com?
10. …Do you see all your Phone's  pictures at iCloud.com?
11. …Have you checked to see if the Apple Account is really really the same on the Mac and at iCloud.com?
12. What is your storage at iCloud.com? At System Settings>[name]>iCloud>Storage , my Mac says 176 GB of 200 GB used. What does yours say?

Let us know…

Thanks for the details--I get it now! All the memory stuff looks fine-- you should not let the "used" get more than 90% of the total.

But I don't have an answer. I "favorite" (a verb?) pictures in Photos on my Mac, and they are immediately (well, that depends on wifi, etc) favorited on my iPhone and at iCloud.com. And it's just as fast the other way-- I just made sure.

So, since iCloud Photos agrees with your Mac, it must be that the iPhone is the weak link. Does favoriting transfer from Mac to iPhone for you?

The "attributes" transfer separately from the pictures, so changes in captions, favorites, etc. may take longer to happen.

On your phone, check in the Collections > ID icon

to see if syncing is paused. Keep in mind that iCloud is designed primarily for mobile devices, and since syncing uses the battery, and since lots of people are very anxious about battery drain, the iPhone will avoid syncing when not plugged in. And since syncing uses processing power, and people hate slow-downs, the iPhone will avoid syncing while you are using it. And since syncing requires bandwidth, the iPhone will avoid syncing when the internet connection is weak.

So, if you want faster syncing, then find good wifi, plug the phone in, and leave it alone.

I’ve had a similar problem since updating to iOS 27 where the photos and favorites, etc., on my phone do not sync properly with the folders in my macOS photos app Specifically, though, any new folder created on iOS 27 did appear on my Mac but not with the photos that I put in it. In other words it was empty. I looked up several remedies for this, and none of them worked until the last one. It was deduced that the database on the Mac even though it was at 27 as well was corrupted. I think I got around that by creating a new iPhoto library making that to default letting it rebuild and then deleting the old one

The iPhone automatically comes out of "Pause" mode when it's plugged in with good wifi. I'm not really sure if the wifi comes and goes--I think it's one of those things that never works if you watch all the time! But I imagine that, if it's plugged in and the wifi comes up substantially strong and stable, the phone will go back to syncing.

Thanks for the reply, Richard. Info you requested is below. I am not transfering photo via USB cable. I just mean if I favorite a photo on my phone, then go to favorites in Photos on my mac, it is not there. But some are. So if I favorite ten photos on my phone, two will be in favorites in Photos on my mac. I guess I also should I have mentioned that this used to work fine, this is something new.

I am using 272GB of 512GB. Battery health: normal, Max Cap: 90%, Cycle Count: 403. Mac storage: 1.1 TB used of 2TB. Only one Photos library and it is in the Pictures folder on my mac. Yes, iCloud to syncronize. Optimize Storage on iPhone is checked, Optimize Storage on mac is checked. On iCloud.com I see the same photos as what is on my mac, so not all of the favorites that are on my phone. Same Apple Account on both devices. iCloud storage is 925GB of 2TB used.

I do have battery power on my iPhone set to Adaptive. Would that have anything to do with it?

With iOS27 and macOS27 the handling of Favorites has changed. The Favorites are now combined with rating stars. That might cause problems if one of the devices does not yet support star ratings.

My devices are all using most recent system versions, iOS27 and macOS 27 and the Favorites are synced properly and instantly, as long as I am using Wi-Fi and are applying the Favorite heart plus a star rating.

"Add titles, captions, and more to photos and videos on Mac - Apple Support

Apply a star rating to a photo or video

1. Go to the Photos app  on your Mac.
2. Double-click the photo or video you want to rate. 
3. Click  in the toolbar, then choose a rating from one to five stars.
4. If you don’t see  in the toolbar, choose Photos > Settings, click General, then select Show Rating Controls."

Thanks again, Richard! I think you might be on to something. I didn't mention it before, but I am on a cross country roadtrip in my campervan, so power (charging) and WiFi have been a bit inconsistent compared to normal. I checked the ID Icon and sure enough it said "syncing paused". So maybe it paused based on some of the criteria you mentioned. I will say, I usually plug the phone in at night, but maybe WiFi was unstable so it didn't come out of the paused sync state. Do you know if it comes out of the pause once it senses stable conditions or do I have to go in an physically click "sync now"?