Apple sends out emails inviting general public to try iOS/iPadOS 15, macOS 12 Monterey, tvOS 15 and watchOS 8.
“The iOS 15, iPadOS 15, macOS Monterey, tvOS 15, and watchOS 8 public betas are now available. As a member of the Apple Beta Software Program, you can help shape Apple software by test-driving pre-release versions and letting us know what you think.”Apple
Beta program: Apple Beta Software Program
Developer:Check feedback and crash reports from upcoming releases.
QA engineer:Test existing apps on new releases.
PM/DM:Prepare apps for new releases, users might expect apps to run flawlessly on new beta versions.