The 'Mobile App Trends 2021' report highlights significant growth in app usage due to the pandemic, with global mobile app spending reaching $112 billion in 2020. Key sectors such as fintech, gaming, and e-commerce have shown varying trends, with fintech installs increasing by 51%, gaming holding 33% of all app downloads, and e-commerce experiencing a major boom in transactions. The report emphasizes the importance of user acquisition and engagement strategies amid evolving market dynamics influenced by developments like iOS 14.