20 But the Lord hardened Pharaoh’s heart, and he did not release the Israelites. 21 The Lord said to Moses, “Extend your hand toward heaven so that there may be darkness over the land of Egypt, a darkness so thick it can be felt.” 22 So Moses extended his hand toward heaven, and there was absolute darkness throughout the land of Egypt for three days. 23 No one could see another person, and no one could rise from his place for three days. But the Israelites had light in the places where they lived. 24 Then Pharaoh summoned Moses and said, “Go, serve the Lord—only your flocks and herds will be detained. Even your families may go with you.”
10 Then the fifth angel poured out his bowl on the throne of the beast so that darkness covered his kingdom, and people began to bite their tongues because of their pain. 11 They blasphemed the God of heaven because of their sufferings and because of their sores, but nevertheless they still refused to repent of their deeds. 12 Then the sixth angel poured out his bowl on the great river Euphrates and dried up its water to prepare the way for the kings from the east. 13 Then I saw three unclean spirits that looked like frogs coming out of the mouth of the dragon, out of the mouth of the beast, and out of the mouth of the false prophet. 14 For they are the spirits of the demons performing signs who go out to the kings of the earth to bring them together for the battle that will take place on the great day of God, the All-Powerful.
Notes and References
"... The fourth trumpet is an allusion to Exodus 10:21–22, the three-day plague of darkness over Egypt (the persecutor of God’s people). Early Jewish literature (Wisdom of Solomon 15–17 in particular) interpreted the plague of darkness to have symbolic significance: exile from the true God; prisoners of darkness. Amos 8:9 is also likely part of John’s reference (in that case, a judgment on apostate Israelites patterned after the plague on Egypt). The fourth trumpet language may also hearken back to the creation account ..."
Heiser, Michael S. The Old Testament in Revelation: Notes from the Naked Bible Podcast (p. 167) Naked Bible Press, 2021