https://thenextweb.com/apps/2020/06/30/google-photos-backup-whatsapp-messenger/

Google Photos will no longer back up images and videos from folders created by messaging apps like WhatsApp and Facebook Messenger — at least for the time being.

Up until now, Photos did that by default, but that won’t be the case going forward. Indeed, users should soon see a notice about the change within the app. That said, the change appears to be temporary (even though it remains unclear until when it’ll last) and won’t affect previous backups.