When we read the context of both verses 11&12 it makes it clear the difference between the OWG Fourth Beast and The Beast Antichrist.
11 "The beast that was, and is not, is himself also the eighth, and is of the seven, and is going to perdition.
12 “The ten horns which you saw are ten kings who have received no kingdom as yet, but they receive authority for one hour as kings
with the beast. 13 These are of one mind, and they will give their power and authority to the beast"
Revelation 17:11-12
As already pointed out verse 11 refers to The Beast as a person since it says "himself" who was also the eighth but of the seven. Going to Daniel 7:7-8 it reads:
“After this I saw in the night visions, and behold, a fourth beast, dreadful and terrible, exceedingly strong. It had huge iron teeth; it was devouring, breaking in pieces, and trampling the residue with its feet. It was different from all the beasts that were before it, and it had ten horns. 8 I was considering the horns, and there was another horn, a little one, coming up among them, before whom three of the first horns were plucked out by the roots. And there, in this horn, were eyes like the eyes of a man, and a mouth speaking pompous words."
Verse seven specifically describes the OWG made up of ten kings.
Verse eight describes the little horn who represents Antichrist and here it says he will rise up from among them and pluck out three horns, or Kings. This is how I came to understand Revelation 17:11 that the Beast is himself the eighth but of the seven.
It makes sense tying it to Daniel 7:8 when the three horns are plucked out of the Ten, leaving seven , but because there are seven the Beast makes it eight.
Then in examining Revelation 17:12 it is separating the OWG, or the Fourth Beast by identifying it as Ten Kings, but continuing to read it tells us that the Ten Kings receive authority for one hour
with the Beast. Notice the separation here? It does describe the fourth Beast as the ten king OWG but it also tells us that it has authority
with the Beast, the little horn of Daniel 7:8 , the one who is Antichrist.
Whew!
That made my brain hurt to try to explain.
Does it make sense how I explained it?