The only restless spirits are the evil ones Christ casts out of people. The human spirit does not wander over the world seeking rest and finding none.
Ghosts are not the restless spirits of the dead hanging around due to some traumatic death events or unfinished business in life.
After death comes the judgement. Believers belong to the Lord and are with Him after death.
Romans 14:8 (New King James Version)
For if we live, we live to the Lord; and if we die, we die to the Lord. Therefore, whether we live or die, we are the Lord’s.
Hebrews 9, for all people v27, and judgement Christ said His people will not come under judgement as in the judgement of hell for their sins.
But only the judgement seat of Christ to determine rewards.
27 And as it is appointed for men to die once, but after this the judgment,
For Christ's church v28, inherits salvation, an eternal life with God.
28 so Christ was offered once to bear the sins of many. To those who eagerly wait for Him He will appear a second time, apart from sin, for salvation.
Evil spirits though when cast out, do wander over the earth in dry places, meaning there is no rest for them, as does still today Satan, who seeks to kill steal destroy all he can. IF they can, they will join forces and try to come back in. If the Holy Spirit is not indwelling the man, it will be empty and they will take residence within again. They miss their old home; they are uncomfortable outside of a body and cannot interact with mankind to deceive others through teaching the doctrines of demons.
Matthew 13
43 “When the unclean spirit is gone out of a man, he walketh through dry places, seeking rest, and findeth none.
44 Then he saith, ‘I will return into my house from whence I came out.’ And when he is come, he findeth it empty, swept, and garnished.
45 Then goeth he, and taketh with himself seven other spirits more wicked than himself, and they enter in and dwell there; and the last state of that man is worse than the first. Even so shall it be also unto this wicked generation.”
Jesus cast evil spirits out from a still unbelieving generation, no doubt HE did this as one of the signs to Israel of His authority over evil spirits. That does not mean all those people afterwards received Him in their hearts as Christ the Savior, the results of which they were in a very sad state later with the Romans with the destruction of 70AD.