iCloud photos not uploading

Hi, I've been trying to switch on iCloud Photos library for 4 days now and the uploading is getting stuck at a very early stage. I have really good upload speed, bought extra storage in iCloud and I only have fewer than 5000 photos. I've switched on and off, toggled on and off, signed out and back in my Apple ID but nothing works.

Uploading has been stuck at "uploading 4650 photos" for more than 2 days now (can't post a screenshot for some reason).

What do I try next?