Here are a few options for a formal executive summary title, depending on the specific focus of your document:
Option 1 (Direct and professional):
Executive Summary: The Relationship Between Social Media Usage and Subjective Well-Being
Option 2 (More analytical):
Executive Summary: An Analysis of the Impact of Social Media on Psychological Well-Being
Option 3 (Concise and formal):
Executive Summary: Social Media Engagement and Its Implications for Happiness
Recommendation: Option 1 is generally the most standard and professional choice for business or academic reports.