There's a lot to unpack in that passage. I know people have different views of scripture, especially Revelation. There are several rules to which I adhere when reading such a prophetic book. One is: In a particular area, if most of the verses are allegorical then the entire passage is likely allegorical. Unless we are told, the Spirit does not flip flop from allegory to actual within the same passage.
So, in the passage above, we see the Euphrates river. John would have known this river and the importance of it. It provided water to people and crops, allowed for trade and commerce between nations, and was essential to regional life as he knew it. Today, we know it as one of the waterways that established the "cradle of life" so its importance stretched even into our day.
Then, in the next verse we see frogs, a dragon, and a beast. This is allegory. Sure, they denote actual things (like the Euphrates) but the references are to their meanings as they relate to the end of the age. So, the Euphrates, too, relates to the end of the age.
The drying up of the waters of the Euphrates is emblematic of the drying up of revelation and insight. This will be (and currently is) a famine of the word of God. They also represent the removal of restraint (also prophesied and what we are currently experiencing) because it restrained "the kings" until it is dried up. At one time, even the unbelievers saw some wisdom in the way of God and His people. This speaks of a time when the people reject the ways of God and His people whole-sale. And so, they are given over to their unrestrained imaginations.
In the whole picture, this is It is Satan in consort with his offspring, the beast, and his enabler, that little horn that speaks blasphemous things against God and against the dwellers of heaven. This is a religious figure who has led astray anyone who is seeking God and lives by the water of life, the Holy Spirit.