So apart from the proof chapters in textbooks and past paper questions, what other resources might be useful for proofs?
24 bilibili videos on proofs:
https://www.bilibili.com/video/BV1ig411a7kd . This is The Great Courses course Prove It: The Art of Mathematical Argument
If you are not familiar with bilibili it's like a Chinese youtube and you can select the different videos in the video selection box:
There are also some books available as ebooks:
Pólya, G., Mathematics and Plausible Reasoning Vol 1 and 2, Princeton University Press, 1954
Franklin, J.; Daoud, A., Proof in Mathematics: An Introduction, Kew Books, 2011
Gold, Bonnie; Simons, Rogers A.. Proof and Other Dilemmas: Mathematics and Philosophy. MAA., 2008
Solow, D., How to Read and Do Proofs: An Introduction to Mathematical Thought Processes, Wiley, 2004
Velleman, D., How to Prove It: A Structured Approach, Cambridge University, 2006
Hammack, Richard, Book of Proof, 2018
Cupillari, Antonella. The Nuts and Bolts of Proofs: An Introduction to Mathematical Proofs, 4th ed. Academic Press., 2013