Apple Tester

You can sign up as a beta tester when public betas are announced. Note that this is not a good idea to use with your primary device, because beta testing mean using buggy software (if it wasn’t buggy it would be released, and thus would not be in beta testing).

You might consider starting here. But remember not to use any of your “production” (daily use) devices in this program, as beta software can and should be expected to fail on occasion.

https://beta.apple.com/sp/betaprogram/