> Did the ITU have any involvement in constructing the Internet? No.
The ITU had a lot of involvement in the CCITT modem standards. (CCITT morphed to be / is part of ITU.) V.21 through V.92 are all relevant for dial up modems.
None of which are relevant the the internet apart from providing some tunnels. The technical standards did not affect much in the osi stack bar the transport layer, which could be run quite happily over anything out there (Cambridge ring, avian carriers, cups and string, flashing lights).
The ITU had a lot of involvement in the CCITT modem standards. (CCITT morphed to be / is part of ITU.) V.21 through V.92 are all relevant for dial up modems.