Here are a few ways to rewrite your title, depending on the specific focus of your work:
Option 1 (Direct and academic):
“The Impact of Institutional Mistrust, Alternative Media, and News Avoidance on Vulnerability to Disinformation in Greece”
Option 2 (Concise and professional):
“Vulnerability to Disinformation in Greece: The Roles of Political Mistrust, Alternative Sources, and News Avoidance”
Option 3 (More formal/research-oriented):
“Determinants of Disinformation Susceptibility: An Analysis of Mistrust, Media Consumption Habits, and News Avoidance in the Greek Public”
Recommendation: Option 1 is the most standard for a research paper or formal policy report.