Restoring from iCloud photos and videos?

See the articles Set up and use iCloud Photos - Apple Support

Change preferences in Photos on Mac - Apple Support

If its Mac , connect it with power outlet , if you are short with iCloud storage upgrade the storage plan the details are in the article Check your iCloud storage usage online or on any device - Apple Support

It all depends which network plan you have been using allocated from internet service provider and network speed , you can check the network speed using speed test by Ookla on the google site , you can also connect Mac with hot spot from your iPhone Use Instant Hotspot to connect to your Personal Hotspot without entering a password - Apple Support

Use an iPhone or iPad to connect your Mac to the internet - Apple Support

Use a mobile phone to connect your Mac to the internet - Apple Support

Instant Hotspot on your Mac - Apple Support

Connect your Mac to the Internet - Apple Support

If Personal Hotspot is not working on your iPhone or iPad (Wi-Fi + Cellular) - Apple Support

What has happened before the "Restoring from iCloud" first appeared? You may be seeing this notification, if iCloud Photos has become disabled, and Photos has to recreate the connection between the thumbnails of the versions in your local Photos Library and the originals in iCloud. Could it be, that Photos could don't find. your Photos Library, for example, if it is on an external volume? Otr that iCloud Photos got disabled, for example after a system update? It would be safer, if you let the "restoring" finish. Keep the Mac up and running, connected to Wi-Fi, and if your Photos Library should be on an external volume, keep it connected.

Make sure, that no Fore Wall or antivirus filter can intercept the connection between Photos and Apple's cloud servers. Check, that you are signed into iCloud Photos in the system Preferences > AppleID < iCloud, and in Photos > preferences > iCloud.