The timeline is more robust than that. We’re not in the Marvel or DC comic or EEAAO infinitely branching universes concept of a multiverse.
There can be branching events like the one that established the Kelvin universe but they are rare and take something of the order of the Romulan Supernova to create.
This is the prime universe of TOS and the other shows. It’s the same wide river of time, but the layers of temporal incursions - both seen in shows and movies and reported by temporal agents - accumulate changes. Tomorrow and Tomorrow and Tomorrow confirmed this.
The key events and their sequences do not change. The kind of differences that are discernible only by deep study are not sufficiently material to be necessary to protect against.