I think we should heed Tolkien’s last known thought on the matter. Per the 2023 The Letters of J.R.R. Tolkien, Revised and Expanded Edition & Letter #283a of 12 January 1966:
“… only one of the silmarils is now visible: … The other two were lost, in the depths of the sea, the other under the earth, until the end of the world.” (my underlined emphasis)
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