Does a security guard at an opera house for music sin because of the nature of his work?

It is not permissible to cooperate in committing forbidden acts in any way that constitutes assistance, for Allah Almighty says: "And cooperate in righteousness and piety, but do not cooperate in sin and aggression." Music and musical instruments are forbidden, except for the drum. The phrase "they deem lawful" indicates that it is originally forbidden.

It is incumbent upon you to leave the job that assists in music, otherwise you are sinful, unless you are in a state of dire necessity, such as not being able to find another job that secures your livelihood and that of your family. In that case, you may remain while continuing to search for another job. "And whoever fears Allah – He will make for him a way out and will provide for him from where he does not expect."