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! 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 at Google workspace and will be released to users “in the coming weeks”. The applications Drive, Calendar, Meet, Docs, Sheets, and Slides will also get new ones appearance: