Windows / Microsoft
Microsoft offer a sandbox for developers. This comes with 90 day E5 licences for testing and development purposes
https://developer.microsoft.com/en-us/microsoft-365/dev-program
You can also create an evaluation environment for their security products
Microsoft Lab for setting up Defender to detect reconnaissance and lateral movement
https://docs.microsoft.com/en-us/defender-for-identity/playbook-lab-overview
This is the resource page for Exam SC-200: Microsoft Security Operations Analyst. The exam itself is not free however the self taught training materials for the exam are free.
https://docs.microsoft.com/en-us/learn/certifications/exams/sc-200
Becoming a Security Engineer
https://docs.microsoft.com/en-us/learn/roles/security-engineer
Useful Resources
Every Windows command
https://www.microsoft.com/en-us/download/details.aspx?id=56846
Windows API calls
https://docs.microsoft.com/en-us/windows/win32/apiindex/windows-api-list
Microsoft's security documentation
https://docs.microsoft.com/en-us/security/
The file attachments blocked by Outlook.
A tour through some of the security internals of Windows from Steve Syfuhs
https://syfuhs.net/a-bit-about-the-local-security-authority
https://syfuhs.net/how-windows-defender-credential-guard-works
https://syfuhs.net/how-authentication-works-when-you-use-remote-desktop
https://syfuhs.net/what-happens-when-you-type-your-password-into-windows