The Find&Replace function was removed from the new editing experience. According to the Confluence Cloud Editor Roadmap:
"_Find and replace
We removed find as this function is also provided by all web browsers. Press Ctrl + F (Windows) or Cmd + F (Mac) to use find.
There is no workaround for replace. If this feature was valuable to you, please let us know._"
Should be extremely useful to have this functionality in our new editor.