Here are a few options for a formal title, depending on the specific focus of your piece:

• The Legal and Political Context Behind the Deportation of Russian Journalist Xenia Fedorova from France
• An Examination of the Factors Prompting France to Deport Russian Journalist Xenia Fedorova
• France’s Removal of Russian Journalist Xenia Fedorova: Official Rationale and Implications

Recommendation: The first option is the most balanced and suitable for a formal report or analytical article.

Here are a few ways to rewrite the title in a formal tone, depending on the desired emphasis:

• France Expels Russian Media Commentator for Alleged Disinformation Activities (Most standard and precise)
• French Authorities Expel Russian Media Figure Amid Disinformation Allegations (Focuses on the state action)
• France Orders Expulsion of Russian Media Analyst Over Disinformation Concerns (Highlights the official legal/administrative nature of the action)

The most recommended version:

France Expels Russian Media Commentator Over Allegations of Disinformation

A more formal way to phrase this title would be:

The Impact of Social Media Misinformation on Public Belief Systems