Interview Presentation - Free Work Before Youre Hired

Curious what your thoughts are on interview presentations essentially being free work before you're hired.

A company is asking me to audit their existing social media ads and website and create a 20-30 min presentation that includes 1) Q1 media plan, budget split 2) tactical recs for paid social creative, messaging, and platforms 3) guide to design a new landing page based on audit of their existing paid social landing pages.
Y'all they said this would take 2 hours - it took me a full day's work ~8 hrs. As a former consultant, this is something I would charge for.

They asked to share the presentation with them BEFORE the interview. Is that normal? They could take my ideas and run. At what point is my work proprietary? How can I approach this to protect my work?