Maybe also the Proj documentations should be checked https://gdal.org/en/stable/drivers/raster/ntv2.html. Now I understand that Proj claims the GTX can be created with GDAL:

PROJ supports the GeoTIFF (Geodetic TIFF grids (GTG)) and GTX file formats for vertical grid corrections. Details about all the formats can be found in the GDAL documentation. GDAL both reads and writes the format. Using GDAL for construction of new grids is recommended.

@Pittu-Sharma I see in your profile you're eager to learn about AI. Fine for you, but here we are more interested in contributors interested about GDAL and geospatial. Reviewing and integrating pull requests mostly driven by AI is an increased burden on maintainers shoulder, so please use responsibily and make sure to follow the directions of https://gdal.org/en/stable/community/ai_tool_policy.html and keep in your pull request summary the check box about AI use and tick it when appropriate