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:
See:
It's just an M! than Mail, but it has more colors of Google. It looks like an envelope, but it's a bit more abstract.
The change comes as part of the rebranding of G Suite to Google Workspace and will roll out to users "in the coming weeks." The apps Drive, Calendar, Meet, Docs, Sheets, and Slides they will also get new ones appearance: