If… the Church says “it is not a sin to drink a glass of wine” and the person still believes it is, and then drinks a glass of wine, I don’t think God will hold them accountable for sinning by drinking a glass of wine.
Probably best for us not to railroad this thread with the Church’s finally balanced teaching on conscience.
I simply one time observe that you are going somewhat against mainstream Catholic teaching with your above comment. If one truly believes something is seriously offensive to God (regardless of what it is) and freely chooses to do that thing knowing this then that is indeed a vicious actual sin.
However, God may hold them accountable for not believing in the Church’s Teaching that it is not a sin to drink a glass of wine.
One would only be held accountable for this if we did not have a “certain conscience” or had taken little trouble beforehand to try and inform our conscience before the act involving a certain (yet allegedly erroneous) conscience.
What does it mean to inform our conscience?
At the most primitive level it means to make an effort to update ourselves on what the Church’s related moral teachings and principles are.
However simply having the Church’s teachings explained to us does not necessarily mean a sincere and blameless conscience will always be persuaded to act objectively correctly.
Things can still go wrong, even with blameless agents.
For example, the Church may not have a specific teaching for this specific case. It may rest on application of principles. Different Church principles may or may not apply to this particular case. In which case wise and sincere Catholics may choose different courses of action and both be blameless.
Or, the Church does seem to have a specific teaching that clearly applies but we just cannot in certain conscience agree with it. For basic, grave moral matters (eg the Commandments whose matter reflects immutable natural law) it would be very unlikely that a sincere and well educated Catholic would ever find themselves in such a position. Some Catholics just cannot see why contraception is always and everywhere sinful. That is understandable as the evil of contraception is determined only indirectly via natural law principles.
Or, some teachings are not in fact immutable moral doctrines but arbitrary but wise Church disciplines that could be changed and usually have already been in the distant past. It is understandable then that they may not apply well in all cases and sincere Catholics who have long questioned their applicability in their situation may in fact be right.
This area can be difficult if the discipline is very very old - such as no Communion for all active irregulars.
So simply “knowing” the Church’s teaching does not mean we are blameworthy for not informing out conscience if our conscience still cannot assent with certainty and we act otherwise.
However a person who has made the effort to inform his certain (objectively erroneous) conscience with correct Church teaching will of course be aware they are materially acting contrary to Church teaching.
In such cases a blamelessly informed conscience will continuously seek wise counsel, likely be a model Catholic in other areas of their lives, and keep possible scandal to a minimum.
In which case God will not hold such persons accountable for “not believing” the teaching in question.