Webarchive cannot be opened because it is from an unidentified developer.

When I save a web page in Safari (Safari > File > Save as > Format: Web Archive), then try to open this saved file I often get a dialog box saying:

“ Filename .webarchive” cannot be opened because it is from an unidentified developer. 

macOS cannot verify that this app is free from malware.

this was not before the update to version 15. now version 15.1 and the problem persists