I wonder how that would have worked had there ever been a Pope-elect who had been castrated.
That was a thing for a while by some early priest & religious monks to show that they were really devote & celibate. It had been common for the priesthood in some other, pre-Christian religions. Possibly that’s why it went out of favor in the Church; by the time of the Council of Nicaea voluntarily-castrated males could not become priests (those forcebily castrated by enemies or as slaves by their masters still could).
Ignoring, as conspiracy theories do, an important detail; it really does not matter if Montini was a cardinal - any man is qualified to be pope. (“Have a seat here and demonstrate your qualifications…”) Montini was more than qualified. I guess the debate - unprovable now - was whether the vote was a majority of the “legitimate” cardinals. (He created 52, including a flurry of 23 the first year).
The “mainstream” sedevacanists don’t claim that John XXIII was falsely elected in place of the real pick Siri. That’s Malachi Martin, as was mentioned. They draw it from a papal bull from the counter-reformation that says that only a Catholic can be pope, and that an active heretic is no longer a Catholic, and also a provision in canon law that says that a priest who renounces Catholicism can no longer serve in a position in the church or exercise priestly functions. Since Vatican II, they say, embraced heretical ideals, like freedom of religion and such, (basically the “modernist” and “Americanist” heresies) , all the participants publicly embraced heresy, and lost their priestly status. So John was no longer validly Pope, all of the cardinals who were at Vatican II lost their status, and Montini was no longer eligible to become pope.
Nah, that’s all a smoke screen. The real sin was outlawing Latin Mass. If they hadn’t done that, then most of those Sedevacantist types wouldn’t have left the church. Oh yeah, allowing guitars in church was a big no-no, too. That was an attempt to stay “relevant” to young people, but it didn’t work, at least not with me.