Since "upgrading" to OS X 10.15.6 I have similar problems with Safari. (MacBook Pro, Retina, 13-inch, Mid 2014). Other browsers work fine, with caveats, see below.
Catalina upgrades are likely to affect Safari because it is a core conduit for the eventual integration across all Apple operating systems.
Apple's O/S software testing has been poor since the introduction of Catalina. They don't do a great job of keeping software partners up-to-date on changes that affect them, e.g. Evernote. As of 2020-06-21 Web Clipper prevents this error message after failing to upload from Safar