What is the ruling on engaging in an action which carries the risk of a physically harmful outcome and is definitely harmful mentally?

Qisas in the matter of a negative outcome is not attainable neither through Islamic means nor through the laws of the (non Islamic) country in which one resides and neither is the harmed person willing to forgive the harm even though it is know to be the best choice?

Should the actio be avoided in order to not suffer harm?

What ayahs or narrations support the avoidance of actions that are harmful to the physical as well as mental and spiritual aspect of a person?

We have the Law of No Harm. The Prophet (s) said: لا ضرر ولا ضرار في الاسلام
“There is no harm and harming in Islam.”
Hence it’s prohibited to harm oneself and others. Doing so is a sin. If one causes harm and sincerely repents, Allah forgives. If one does not repent and gets away with it in this life, Allah will hold him accountable in the Hereafter.