Protonmail Icons and Graphics (including Wallpapers) - eviltoast
Proton media kit | Proton
protonmail.com
The Proton media kit includes brand images, product image (Proton Mail, Proton Drive, etc), and media assets that are freely available to use.

Looking for a nice wallpaper for your desktop?

Protonmail has quite a few available on their site, plus some other graphics and icons