Do I need to confess objectively grave sins?

I know that we have to confess all known mortal sins while in the sacrament of confession, but do we need to confess sins that are objectively grave, but subjectively venial? If I didn’t know that a sin was grave or I only had partial consent (thus taking away its mortal nature) would I still be required to confess it?
God bless

Code of Canon Law:

Can. 988 §1. A member of the Christian faithful is obliged to confess in kind and number all grave sins committed after baptism and not yet remitted directly through the keys of the Church nor acknowledged in individual confession, of which the person has knowledge after diligent examination of conscience.

If someone lacks culpability then they did not commit a grave sin and thus do not have an obligation to confess it. However, given the difficulty we all face in truly assessing our own culpability the general rule of thumb is that we should confess sins that are objectively grave.

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