I've been struggling with previous versions also. My use case is to install previous versions on Parallels. So far, what I've found is:
https://developer.apple.com/download/
"macOS Sonoma", "macOS Ventura" in the app store
https://ipsw.me
https://ipsw.me/Mac15,7 worked for me, where the other two didn't. Unfortunately, ipsw.me aren't "official" images.
-mikael
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