Security is always important at every stage of development. I've worked with Agile teams, and integrating security into the process has always been a challenge. Agile security practices, which you can read about here https://www.jappware.com/insights/agile-security-in-action-our-approach-to-delivery/, really help catch issues early without slowing down development. I like how it promotes continuous testing and collaboration between developers and security teams instead of treating security as a final step.