Bisnis write gobernment plan underwater tunnel toll road to connect Balikpapan–Samarinda (Balsam) with State Capital or IKN Nusantara. I think more probably immersed tunnel what I understand press conference of head of Toll Road Regulatory Agency (BPJT) on 24-1-2022.  BPJT head say project is yet in detailed technical planning stage (Detail Engineering Design).

https://ekonomi.bisnis.com/read/20220124/45/1492615/pertama-di-indonesia-pemerintah-akan-bangun-tol-bawah-air-menuju-ikn-nusantara