The Gmail folder is one of the most well-known application logos of all time. This will change in a little while for a much different logo:
It's just an M! from Mail, but has more Google colors. It looks like an envelope, but it's a little more abstract.
The change comes as part of the redefinition of G Suite in the Google Workspace and will be released to users "in the coming weeks". Drive, Calendar, Meet, Docs, Sheets, and Slides will also get a new look: