@PetrW
By the way, it is not Sheol / Hades that is fiery, but Gehenna is. The King James Version caused lasting confusion by translating both Greek words hades and gehenna as “hell.” This is often reflected in older liturgical texts which say that "Christ descended into hell." So Jesus was in Hades, every Christian who knows the Apostles' Creed knows it. While Jesus was dead, the human soul descended into "Hades", within that to Abraham's bosom, also known as “paradise”, also known as "limbus patrum". Acts 2:27 specifically says that Jesus' soul (psyche) went to Hades. Acts 2:27 says Jesus' soul _WAS_ in Hades, and Eph 4:9 says that He descended to it. You only have to read these two verses together and you will get what the Apostles' Creed contains.
Since the two verses report on the SAME event (what happened to Jesus between his bodily death and his resurrection, and this is what 1 Peter 3:18-19 and 4:6 also talks about), it is therefore simply necessary to read these parts TOGETHER.
According to this, when Jesus died, while the disciples put his body ('soma') into the tomb ('mnemeion'), but his soul ('psyche') descended to the underworld ('hades'), and within that to the "part" of it, which was called on the one hand "paradise" ('paradeisos', Lk 23:43), on the other hand "Abraham's bosom", and in Latin theological language it was called 'limbus patrum'. And here he proclaimed the gospel to the spirits of the DEAD in "prison" (that is, in sheol) and set them free, that is, as Ephesians 4:8 says "when he ascended, he took many captives" (with him to the heaven), he therefore took the righteous of the Old Testament times to heaven, only then did the closed gates of heaven open.
1Peter 3:19 - here it is clearly not about (fallen) angels, since 4:6 clearly calls them deads, and the Scriptures always only call people dead. Besides, why would Jesus have preached the GOSPEL to the fallen angels in 'hades'? Furthermore, according to Ephesians 4:8, Jesus took these imprisoned spirits into heaven with him.
In 1 Peter 3:13-22, Apostle Peter offers consolation in persecution, and to strengthen them in the sufferings of persecution, he points to Christ, who was killed in his body for our sins, but his soul was revived or enjoyed the beatific vision of God due to his personal unity with divinity. At the moment of his death, his sacred soul descended to the souls in prison, or the porch of hell, where there were also the souls of those who did not believe in Noah's call to repentance while the ark was being built, but in the face of impending danger they turned to God. He preached redemption to all of them, which was completed with his death.
The meaning of verses 19-20 is this: After the death of his body, the soul of Jesus descended to the underworld, not only to the holy patriarchs but also to the unbelievers who, while the ark was being built, did not believe God's threats, but when punishment came upon them, they found salvation in faith and repentance. Christ proclaimed to these righteous forefathers, and to these once unbelievers but later converts, that he had completed the redemption and opened the gates of heaven. Before Christ died, all the souls of the dead, both the good and the bad, went to the underworld. But this was separated in itself (Luke 16:26) so that the righteous went to a place where they awaited the Redeemer, while the wicked were pushed to the place of eternal torment. This is properly called hell, while the former is called the limbo of hell, which also existed in the underworld, but at the same time was a purgatory for the heaven. The underworld (Genesis 4:16,30,33), where all the dead gathered (Job 30:23) before Christ had completed his great work, was indeed a place of prayer for the wicked (Job 26:5.), but for the righteous too, as the limbo of hell, it was not a place of joy, but of silent sorrow (Psalm 30:10. 87:13. Isaiah 38:18. Ecclesiastes 9:10), and in this respect it was not that place where God is exalted and praised, as on earth. Only through Christ did death cease to be sad, because he opened heaven, the place where God is exalted and praised. When the Apostolic Creed says: "descended into hell," this does not mean the actual hell, the place of punishment for the damned, but the underworld, into which Christ descended insofar as he appeared in its part, in the limbo of hell. Apostle Peter calls the limbo a prison because souls were kept there until the coming of Christ. That's why it talks elsewhere (Acts 2:24-25) about the chains of Hades. Under the unbelievers, some understand those who died in unbelief and wickedness, to whom Christ proclaimed repentance to convert them, or at least some of them. According to others, these were irretrievably damned, whose condemnation Christ confirmed. This latter opinion is unlikely, because confirmation of damnation is not preaching, especially not the gospel (good news), as Christ's teaching here is called in 4:6.
The first opinion cannot be accepted because there is no salvation for those who die in unbelief, i.e., outside the grace of God. However, the Church Fathers and older Bible interpreters, correctly understanding the words of the text and comparing them with the teaching of Scripture in this regard, found a suitable solution. Since, on the one hand, the text only speaks of such unbelievers who were unbelievers at the time when the ark was being built, and it does not exclude that these unbelievers could still repent before their death; on the other hand, because the clear teaching of Scripture stands that the one who dies in unbelief can do nothing more for his salvation, - so we must understand such unbelievers who did not persist in unbelief and sin, like the monstrous rebels at the time of the flood (Job 26:4), but who by repentance and contrition did not physically, but at least spiritually saved their lives. Furthermore, the text says: Christ preached also to those who were once unbelievers, so he preached not only to these unbelievers but also to others, i.e., to all the ancient righteous and saints; because the word "also" cannot refer to people living on earth, because it is not Christ who taught on earth, but Christ who preached in the limbo. The fact that Peter does not mention these righteous here, but only mentions these unbelievers, is particularly explained by the opinion generally held among the Jews at the time, that those who perished in the flood were completely rejected by God, and could not even appear in public life. The baselessness of this opinion could not be better illustrated by Peter than by bringing up from those unfortunate ones who Christ proclaimed the redemption. These are in the best agreement with the context. Since it is said of Christ that he died a violent death bodily for the sins of others, but preserved his spiritual life: so it is quite appropriate to talk about those who died violently bodily for their own sins, but saved their lives spiritually. In addition, they serve as special examples for the peaceful endurance of life's sufferings, to which Peter advises above.