The next annual holy day after Trumpets is Atonement.
Atonement is listed with the other holy days in Leviticus 23:1-44. "Also the tenth day of this seventh month shall be the Day of Atonement. It shall be a holy convocation for you; you shall afflict your souls, and offer an offering made by fire to the Lord. And you shall do no work on that same day, for it is the Day of Atonement, to make atonement for you before the Lord your God. For any person who is not afflicted in soul on that same day shall be cut off from his people. And any person who does any work on that same day, that person I will destroy from among his people. You shall do no manner of work; it shall be a statute forever throughout your generations in all your dwellings. It shall be to you a sabbath of solemn rest, and you shall afflict your souls; on the ninth day of the month at evening, from evening to evening, you shall celebrate your sabbath" (Leviticus 23:27-32).
The Day of Atonement is a holy day, an annual sabbath, and the Church of God rests on that day, assembles for services, and fasts on that day (no food or water for 24 hours, from sunset to sunset).
It is interesting that there are eight commanded annual days of observance listed in Leviticus 23 where the Church is to hold services of some kind: Passover, the first day of unleavened bread, the last day of unleavened bread, Pentecost, Trumpets, Atonement, the first day of the Feast of Tabernacles, and the Last Great Day. Yet there are seven feast days and seven holy days (a holy day is an annual sabbath, a day of commanded rest).
Passover is a feast day, but not a holy day. We can work on Passover day. Atonement is a holy day, but since we are to eat no food on Atonement, I don't think it is to be considered a feast day.
We know from the account of the two goats in Leviticus 16:7-31 and from Revelation 20:1-3 that one of the meanings of Atonement is the putting away of Satan after Christ returns. The goat that is killed represents Christ and the goat that is released in the wilderness represents Satan.
But Atonement has a dual meaning. It also, like Passover, represents the sacrifice of Christ for our sins and the forgiveness and reconciliation with God that that sacrifice makes possible.
It addresses the question, who is responsible for our sins, Satan or ourselves? Are we responsible for what Satan tempts and deceives us into doing?
The answer is, both. Satan has his share of responsibility, and he is banished as a punishment. But we also have a responsibility for yielding to Satan's temptations, and our penalty is death. But Christ paid the penalty for our sins so we can be forgiven.
The account of the two goats does not indicate that Christ pays the penalty for Satan's sin. Satan bears his own penalty.
After Christ returns, Satan will be put away in a condition of restraint and not allowed to deceive and tempt mankind anymore. For the first time in the history of mankind, the earth will be free from Satan's influence.
This is one reason why the millennium, represented by the Feast of Tabernacles, will be a time of peace and joy over all the earth.