It only affects undocumented behavior, no documented behavior is being broken.
If you want to consider breakage of undocumented / unintended behavior as a major change, then every bug you fix would require a major version bump, since when you fix something you are essentially breaking compatibility for anyone who might have possibly relied on the existence of that unintended behavior.
You can argue the correctness or not of the guidelines put out at semver.org, but I don’t think there’s any room to argue that announcing a 1.x with a change the developers say is a breaking change, which is what Immich have done, fits within the semver.org guidelines.
The API specification is unaffected by this.
It only affects undocumented behavior, no documented behavior is being broken.
If you want to consider breakage of undocumented / unintended behavior as a major change, then every bug you fix would require a major version bump, since when you fix something you are essentially breaking compatibility for anyone who might have possibly relied on the existence of that unintended behavior.
You can argue the correctness or not of the guidelines put out at semver.org, but I don’t think there’s any room to argue that announcing a 1.x with a change the developers say is a breaking change, which is what Immich have done, fits within the semver.org guidelines.