I would say its more suprising that ProtonMail shows up in a movie like Knives Out (which has no technical content), than it is for it to appear in Mr. Robot (a purposefully technical series, and being underwritten by Michael Bazzel, who is an advocate of ProtonMail).
mr robot is uncommonly good about depicting technology and security practices. it also shows elliot booting into kali linux, despite most viewers having no idea what that is.