There is an issue with Safari syncing currently. It can affect certain devices and not others, my iPad Pro and my iPhone 7 do not sync Safari history, or I should say History does not sync to them from my other devices, a MacBook Pro and an iPhone 11 Pro Max. Those two sync properly between each other. This will affect your Frequent sites as well as Siri suggestions. It does take a couple days after signing out of iCloud for Frequent sites to reappear, especially if any other devices on that iCloud account are not syncing Safari history to that device. You will only get local sites eventually appearing as Frequent sites. Some people become aware of the issue when they notice that Safari tabs do not sync properly. This started for me on that ipad and iPhone 7 when 13.0 was first released and has not been resolved as yet on the 13.3 beta.