The sound itself is not dangerous. Tinnitus is a perception generated by your brain, not a sign of ongoing damage. It does not cause hearing loss, it does not harm the ear, and the loudness of the ringing does not correlate with the severity of any underlying condition. People who have had bad tinnitus for thirty years do not have worse ears as a result of the tinnitus.
What can be dangerous is the distress that goes with it. Chronic tinnitus is associated with higher rates of depression, anxiety, sleep disturbance and, in severe cases, suicidal thoughts. That is the layer that needs taking seriously, and it is the layer that responds best to treatment.
There are a few presentations that do warrant a prompt medical workup: sudden hearing loss in one ear, pulsatile tinnitus (in time with your heartbeat), tinnitus paired with severe dizziness or unsteadiness, and tinnitus only in one ear that came on quickly. These are not dangerous because of the sound — they are flags for underlying conditions worth diagnosing.
If you are struggling with distress, please reach out. Help lines and crisis support are listed in Resources.