With someone of such profound responsibilities, he may have been troubled by the thought of how he might have made mistakes.  He was a bit on the liberal side in some respects, and the Modernists pounced on his Encyclical Providentissimus Deus to exploit some passages that were easily hijacked and misinterpreted.

He was responsible for every bishop he appointed.

I know that THE number one responsibility of a pope is to appoint good bishops.  If I were Pope, I would do little else besides personally see to a staunch Traditionalist bishop in every diocese.  Then condemning errors that required condemnation.  No audiences (except for choosing bishops), no public speeches, no travelling tours, etc.  Certainly in every diocese one could find a solid Traditionally-minded priest to elevate to the episcopacy.  Too often, however, popes just selected those with the right "credentials," those who studied at the right schools and got the right degrees.  Huge mistake.  Pope Pius XII did the poorest job of all, appointing nearly every bishop that would give us Vatican II.  He went with the guy in each diocese who had the degree from Rome and those with the right "pedigrees".  I would pick the most holy and well-educated priest who could be found in each diocese that was a staunch Traditionalist.  I would select a St. John Vianney to be a bishop over any of these guys with their degrees.  I would personally find and investigate every single potential candidate, and I would remove all the bad ones.  If I even sniffed the slightest bit of liberalism, he'd be gone.  And I would also be doing an act of charity for him by doing so.  Of course, nowadays, the first official act of a Traditionalist Pope would be to immediately depose EVERY SINGLE Conciliar bishop, and then possibly rehabilitating a couple here and there, like a Bishop Schneider.  But I think the number that remained of the Conciliars could be counted on one hand.

Pope Pius XII's corpse exploded after his death.  Although we know the cause, an absurd alternative preservation method, it could also be seen as a sign from God, as Pius XII allowed Modernism to flourish absolutely unchecked by any countermeasure and appointed nearly every bishop during his lengthy reign that would bring us Vatican II.

Yes, here's one treatment of it, but you can find more by Googling for "Pius XII corpse exploded".
https://medium.com/the-collector/explosion-of-pope-pius-xii-e9151906929

We know that the natural cause was the ridiculous embalming job of Galeazzi-Lisi, but still makes me wonder.
https://en.wikipedia.org/wiki/Riccardo_Galeazzi-Lisi
I personally believe that Pius XII was being poisoned during his last 5-6 years.  During that time, he was almost completely debilitated and letting the Curia run the Church, and it's possible that the Holy Week Rites were pushed through with little complicity on his part.

Yeah, while we know the natural causes of this problem, everything that happens takes place by God's will.  God allowed Pius XII to select Geleazzi-Lisi to by his physician and then request that his organs not be removed, etc.

Pope Pius XII did in fact usher in the Vatican II era:

1) failed to consecrate Russia to the Immaculate Heart of Mary in the manner that Our Lady requested
2) opened the door to evolution (which has led to a massive loss of faith among Catholics)
3) opened the door to the use of NFP as Catholic Birth Control with some ill-advised speculation and complete lack of clarity regarding the principles, just using a vague term "serious reason"
4) set up Bugnini to begin his liturgical experimentation (even Roncalli kicked Bugnini out)
5) allowed some bizarre one-off liturgical experiments
6) permitted the first "Ecuмenical" meetings
7) allowed Father Feeney to be persecuted while doing nothing about the rampant heresy regarding EENS, from the likes of Cardinal "No salvation outside the Church? Nonsense" Cushing
8) did nothing to stamp out Modernism and remove Modernists from their teaching positions
9) appointed, during his long reign, nearly every single Bishop would later bring us Vatican II

His was indeed a watershed papacy, and his "after me, the deluge" quote was prophetic, except that he knew it was coming because he had seen it unfold in front of his eyes but took no action to stop it.  I think that he was in fact the "Fatima Pope" (having been consecrated a bishop on the exact day of the miracle of the sun), but not for good reasons.  He was the Pope of whom Our Lord complained to Sister Lucy that they were following the example of the Kings of France (who refused to make the consecration of France to His Sacred Heart).  He was the Pope that was SUPPOSED to make the consecration, but failed to do so.  And the aftermath of his papacy was what was being warned about in the Third Secret.  Had he simply complied with Our Lady's request to perform the consecration in the manner that she requested, Vatican II and the loss of millions of souls that resulted would not have happened.  It's terrible to think about.