Turn screenshots and other PNG images into HEIC, which usually takes less space. Rename the file in Finder and Renamable converts it right where it is. Nothing is uploaded.
PNG.png
iPhone photo.heic
Screenshot.pngScreenshot.heic
Yes
How to do it.
Select Screenshot.png in Finder and press Return.
Change .png to .heic and press Return. If Finder asks, choose “Use .heic”.
Renamable converts it right there. The original goes to the Trash, or stays next to the new file if you prefer, and you can undo any conversion.