1. Local PC
Tests are generally supported 1 to 3 weeks after a new OS version is released. While pre-release beta versions are not officially supported, they often work. You can try using the beta version, and if issues occur, support will be provided as much as possible. However, resolving issues, especially with major beta versions, may be challenging in the short term.
2. Cloud devices
Tests are typically supported 3 to 5 weeks after the latest OS version is released. Major versions are always provided, but minor versions are only added every 2 or 3 updates. For example, if iOS 15.0 is supported, then iOS 15.2 and 15.3 may be added, but not iOS 15.1. Currently, pre-release beta versions are not provided, though there are plans for future support.
3. External cloud services (BrowserStack/SauceLabs)
If an external cloud service provides the latest OS version, testing may be possible, including for beta versions. The support duration varies by service, but it is typically available within 1 to 3 weeks after the version becomes usable.