I would point you in the direction of "Leadership - Theory & Practice" by Peter G Northouse.
This book contains an absolute wealth of resources, references and work on leadership, theories, styles, models etc. It is updated regularly (8th Edition I think) so will also have contemporary content.
Here are some new articles on leadership theories:
1. Da’as, R., & Zibenberg, A. (2021). Conflict, Control and Culture: Implications for Implicit Followership and Leadership Theories. Educational Review, 73(2), 194–208.
2. Jaser, Z. (2021). The connecting leader Aligning leadership theories to managers’ issues. Leadership, 17(3), 376–382.
3. Sawan, F., Suryadi, & Nurhattati. (2020). Servant Leadership: Antecedent Factors, Impact, and Education Theories Used as Researcher’s Perspective. International Journal of Higher Education, 9(5), 60–75.
4. Swanson, S., Billsberry, J., Kent, A., Skinner, J., & Mueller, J. (2020). Leader prototypicality in sport: The implicit leadership theories of women and men entering sport management careers. Sport Management Review (Elsevier Science), 23(4), 640–656.
5. Gardner, W. L., Karam, E. P., Alvesson, M., & Einola, K. (2021). Authentic leadership theory: The case for and against. The Leadership Quarterly.
- MARIA VASILESCU (2019) LEADERSHIP STYLES AND THEORIES IN AN EFFECTIVE MANAGEMENT - ACTIVITY, Annals of the „Constantin Brâncuşi” University of Târgu Jiu, Economy Series, Issue 4.
Gardner, W. L., Karam, E. P., Alvesson, M., & Einola, K. (2021). Authentic leadership theory: The case for and against. The Leadership Quarterly, 101495.
Harrison, C. (2017). Leadership theory and research: A critical approach to new and existing paradigms. Springer.
Bäcklander, G. (2019). Doing complexity leadership theory: How agile coaches at Spotify practise enabling leadership. Creativity and Innovation Management, 28(1), 42-60.