you are correct - Jerusalem is the great harlot-city referred to in the book of the Apocalypse
“The great” as in “Come, I will show you the judgement of the great harlot” (Apoc. 17:1) refers to Jerusalem. This makes it clear that the harlot city, the woman on the beast is Jerusalem.
God’s judgement is on the city that “shed the blood of saints and prophets” as seen in John’s day - this echoes Jesus Christ’s own words when He spoke of Jerusalem “O Jerusalem, Jerusalem, killing the prophets and stoning those who are sent to you... Behold your house is forsaken and desolate” (Matthew 23:37-38)
We see the same in Isaiah 1:21 “How the faithful city has become a harlot, she that was full of justice! Righteousness lodged in her, but now murderers”
As you pointed out we have Apocalypse 11:8, 16:19, 17:18 referring to the harlot as the “great city” where the Lord was crucified.
It is also clear that the harlot rides the beast that later devours her — imagery of Jerusalem riding the Roman Empire which ultimately devours her
I suppose it’s completely understandable that you would fail to see Rome in that prophecy.
Others have seen her in it, though. Keep that in mind, lest you be caught up in the delusion.
I don’t believe a word of it, we are not talking about Babylon but mystery Babylon.