Can "Fake News" be used as a propaganda tool to strategically impact an elections outcome? Is it proven to change peoples mind regarding what they're voting for?
Yes. Europe saw this before and during the two World Wars. The nazi NSDAP party lead by Hitler won a democratic election in 1932 in Germany largely due to an extensive propaganda effort.
The trust in the usefulness of propaganda against a people as a tool leading up to the 2nd World War - mainly by spewing faults, hatred and blame on certain demographics such as Jews and disabled individuals in order to justify the coming war - lead to the Nazi party creating an entire propaganda ministry as part of government:
Once in power the Nazis took control of the means of communication by establishing the Reichministerium für Volksaufklärung und Propaganda ('Ministry for Popular Enlightenment and Propaganda') - or RMVP, under Dr Joseph Goebbels.
Still, nowadays, the spread of propaganda or "fake news" is militarized. The latest example I could find is alleged Russian interference in the ongoing Ukrainian election through the spread of fake text messages to peoples phones: https://twitter.com/loogunda/status/1105623757119504384