My question is related to gunah e kabira like being in na-mehram relationship, lying, etc. Especially when the person knew they were doing gunnah but couldn’t restrain, had fear in heart but were somewhat trapped.

If a person has the fear that disclosing their sins for punishment will lead to discomfort, and they seek direct forgiveness from Allah Almighty with a pure heart, and restrain from any gunah, is it acceptable?

Or should the person get punished for act of zina, in order for their tauba to be accepted by Allah Almighty?

No you should not disclose the sin but ask sincerely from Allah for repentance