There is no single (or simple) solution here. Microsoft communicates changes via various channels, such as the Message center, M365 Roadmap, blog posts, etc. And sometimes changes simply roll out unannounced. The staged rollout/first release functionality you are referring to above only applies to new features, not disabling existing functionalities or security-related changes.
That said, the TLS deprecation has been communicated on multiple occasions over the past few years, including via multiple Message center posts. So at the very least, make sure someone is paying attention to those.
How to test the rollouts that MS pushes out the M365 tenant?

Hi everyone,
With Microsoft 365, we can sign up for an early release so that our organization can receive updates first. We can designate that only certain individuals receive the updates.
However, some features only roll out on a per-organization basis. This means that the entire organization will receive access to the feature at the same time. For features like this, it's not possible to selected users in the targeted release program to get the feature early. This means that our organization will not be able to receive these features early for testing purpose even if we have configured selected users in targeted release. A similar incident happen just recently where MS disabled TLS 1.0 and TLS 1.1 which caused any outlook emails to be sent out. Our organization was completely unable to send emails through outlook due to this issue.
How do we make sure that this kind of issue is avoided in future and what is the best practice approach that we must follow?
Regards,
Prabinesh
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Vasil Michev 66,601 Reputation points MVP
2022-09-08T13:39:06.79+00:00 0 additional answers
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Thank you Michev