Search inputs are synced accross applications, how to disable? A colleague of mine has macOS 10.15 (Catalina) and complained about the following thing: He uses the search bar in Mail and searches for something. Then in Xcode he presses CMD+F and sees the same email address there as the search input. We have checked and that is not in the system clipboard.

This synchronization of search strings might be a helpful idea, but in practice it does not make sense to search for things across applications. Is there some way to disable this behavior?
Search input uses the same 'hidden' copy buffer that unix uses in Terminal, called the 'kill ring'. The 'kill' command has a second part, called 'yank'

These are used on text editors/terminals/emacs etc using  Ctrl ⌃   K  &amp;  Ctrl ⌃   Y 

In effect they are copy &amp; paste, they just save to a different buffer than the regular. As far as I'm aware you cannot disable them, only replace the content with the next 'kill', the same as the regular  Cmd ⌘   C  &amp;  Cmd ⌘   V  copy/paste.

How to Geek has a good explanation of how to use it, though not hot to disable it.
How to Use macOS’ Built-In “Kill and Yank” as an Alternative Cut and Paste