Venial Sin and Admittance to the Sacraments

When I was a child a young man in the parish killed himself.
My mother was the funeral soloist for the parish, and I remember hearing her say that when she was young he would not have been buried from the church because suicide was a mortal sin, and she was glad that was no longer the case.
For now, the Church was more wise in the ways of psychology, and therefore more merciful, as She realized that there was no way to know if someone "could help it," or even if he could, that he had not changed his mind at the ultimate moment, when it was too late for his body, but not his soul.

So Mother Church's thinking on what sin is venial and what is mortal can change, no?

Cannot those with unconfessed venial sin receive communion?
I have always understood that to be the case.

And doesn't Aquinas teach that, although it is objectively grave, under some circumstances adultery might be a venial sin?

It seems that that might be a less contentious avenue to explore than some paths the synodal fathers are on just now...