I think there is a possibility that priests knowing the temple was about to be captured, hid it somewhere. It probably will never be found.
Also possible that it ended up in in Ninevah or Babylobn and then was probably eventually captured by Alexander’s men or maybe destroyed for it’s precious metals soon after it was originally taken.
Read the Sign and the Seal.
The Ark disappeared from Biblical reference during the reign of King Manasseh. Manasseh profaned the Holy of Holies in the Temple with pagan images. The presence of pagan idols next to the Ark of the Living God would have been the worst of blasphemies. The Levites spirited the Ark out of Jerusalem at this time long before the Babylonian captivity and took it to Lake Tana in Ethiopia. From there it wound up in the Church of St. Mary in Axum.
I believe this. There are too many weird connections with the Ark in the Christian Orthodox Church of Ethiopia and Manasseh was the most evil of the kings of Israel.
The story about the Queen of Sheba and Menelik is probably apocryphal.