Most prophecies from God, in the Bible and even today, are “conditional.”
Basically, if things keep going the way they are going, X will happen. X can be a good thing or a bad thing.
In general, God gives us free will. So if God sends Jonah to Nineveh to predict that Nineveh will be destroyed, God is hoping that people in Nineveh will listen, repent, and not have to be destroyed. Repenting changes the conditions, and a good thing happens instead.
It is also possible for God to ask a prophet to prophesy a good thing, hoping that the hearer of the prophecy will be encouraged by the good prediction to do good things. If any person involved doesn’t take the prophecy the right way, it changes the conditions and a bad thing (or even a different but less good thing) happens instead.
Finally, it is also possible to misinterpret a prophecy. God likes wordplay. If God has a prophet predict to me that I’ll always have plenty of meat until the end of my life; and I am a wicked person anyway, and then I mock God’s prophecy; it’ll serve me right if God kills me by smiting me with a side of beef, and I’m smooshed flat by “plenty of meat till the end of my life.”
Or it might be a good thing. Somebody might say, “God told me that Bob the atheist will become a Holy Father.” Well, what if Bob the atheist doesn’t become Pope, but he gets Baptized and becomes a good Catholic holy father of kids? The prophet might have been wrong about how to interpret what God told him, but the prophecy would still be literally correct.
Or somebody might say “Bob the atheist will become a priest.” Every baptized Christian is a priest, prophet, and king in a small way, so the prophecy wouldn’t be wrong; it would just have been fulfilled in a small way instead of a big Father Bob the parish priest way.
And of course, it just might not be fulfilled yet. If Bob the Catholic Dad’s kids grow up, his wife passes away, and he goes to seminary, he might yet become a parish priest or the Pope.