@Dottard answered the first part of the question, the widespread agreement on the identification of the kingdoms with the parts of the statue. I will tackle the second part: a partial refutation of postdiction.
Antiquity. I do not believe that there is sufficient archeological evidence to prove that Daniel was written before the Medo-Persian and Greek empires, though I believe that to be so. However, the Dead Sea scrolls contained fragments of Daniel, showing it to be - at the latest - written in the late second century BC, before Rome conquered the Mideast.
Two Legs. The details concerning Rome are more profound than most people realize. Like two legs, Rome was ultimately divided into the Eastern Roman Empire (Byzantium) and the Western Roman Empire. Later on, it splintered into many brittle pieces, like the iron mixed with clay described in the prophecy.
Ten toes. The number ten symbolizes human (as opposed to divine) completeness, so the ten toes represent all the countries that split off from that empire. That list of coutries is many more than ten, but what if you only count those with overseas colonial empires?
- Portuguse Empire
- Spanish Empire
- French Colonial Empire
- Dutch Empire (Netherlands)
- Danish Empire (Denmark, which submitted to the Holy Roman Empire briefly)
- German Empire
- Belgian Empire
- Italy (in many incarnations: Venice, Florence, etc)
- British Empire
- United States of America (with peoples drawn from all the other European empires)
The above list of ten empires excludes Russia and Sweden, which were never part of the Roman Empire, and some Eastern European empires, which had no overseas possessions.
Between 1492 and 1914, Europeans conquered 84 percent of the globe (https://www.foreignaffairs.com/articles/europe/2015-10-07/how-europe-conquered-world#:~:text=Between%201492%20and%201914%2C%20Europeans,This%20was%20not%20inevitable.) Put another way, they conquered or extended influence over every nation except Saudi Arabia (technically held by Britain during the mandatory period), Japan, Korea, Thailand and Liberia. Even with these, the US occupied half of Korea during the Korean War and afterwards and had influence in Liberia. And after the US defeated Japan in WWII, the US imposed Democracy upon them and denied them the ability to reconstruct parts of their military.
In Revelation it says:
The ten horns you saw are ten kings who have not yet received a
kingdom, but who for one hour will receive authority as kings along
with the beast. (Revelation 17:12)
Daniel says this about the ten kings:
23 He gave me this explanation: ‘The fourth beast is a fourth kingdom
that will appear on earth. It will be different from all the other
kingdoms and will devour the whole earth, trampling it down and
crushing it. 24 The ten horns are ten kings who will come from this
kingdom.' (Daniel 7:23-24)
Thus you see that Daniel's prophecy declares that offshoots from the fourth kingdom would be given great authority over the world. Those conquests would not begin until two thuosand years after Daniel lived. So no postdiction here!