Rollback is available only if you have upgraded the agent by using the UI at least once. You can rollback only to the last version that was used. However, you cannot rollback to a version prior to the just rollbacked version.
For example, if you upgrade Database Agent from 24.1.0 to 24.3.0, and then to 24.4.0, you cannot rollback to 24.1.0. You can only rollback to 24.3.0.