Hey there, Unabletodelete.
Welcome to the Apple Support Communities! Thanks for posting about not being able to completely remove your online web history within Safari. We'd be glad to see how we can help.
Do you happen to use any sort of managed profiles on your device or do you have content restrictions set up? Also, just to verify, is this an iPhone or a Mac? We ask because it's posted in the Mac forum but the post mentions iOS 15, which would be for iPhone.
If this is an iPhone related problem, make sure you've followed the steps in Clear the history and cookies from Safari on your iPhone, iPad, or iPod touch and checked in Settings > General > VPN & Device Management. You can also check Settings > Screen Time for any restrictions that may be disallowing deletion of specific content.
Take care.