Photos on Mac not downloading from iCloud

I have the problem that the Photos app on macOS is not downloading photos taken with an iPhone. Sometimes it works and new photos appear soon after taking them, but most of the time it just says "Last Synced at several hours ago" in the bottom of the photos library.

I have verified that the Photos got uploaded to iCloud, and they do appear on icloud.com. It is on an Intel MacBook Air 2020, and the problem also appears when the battery if fully charged, it is connected to power, WiFi connection is stable, no other applications other than Photos are open. Both the Mac and iPhone are set up to sync with iCloud. It is on macOS Ventura 13.3.1, Photos 8.0 (541.0.120).

I have tried relaunching Photos, and logging in and out, rebooting, but it doesn't help. Usually the Photos only appear the next day.

In Terminal with the command "btctl log -w", the following new output appears when opening Photos (see attachment).

It seems to concern the iCloud synchronization and shows several errors, but says nothing about Photos specifically.

I have tried logging out and back in to iCloud on the Mac (in System Settings). After this it took a long time to resync all the Photos (possibly uploading/downloading again, even though they were still both on iCloud and on the Mac).

Now the problem is still there, but instead it always says "Syncing 11 Items to iCloud - Pause" in Photos below the library, which does not seem to progress since more than 2 days. Clicking Pause and then Resume does not seem to do anything, and produces no output from "btctl log -w".

Is there any way to force Photos to download new photos from iCloud, or to debug where the problem comes from?