The texture-compressor
tool is for KTX v1, which is older and more difficult to use on the web.
Instead I would suggest KTX v2 (which supports smaller Basis formats). You can convert textures using the CLI, C++, or WASM libraries found on GitHub - KhronosGroup/KTX-Software: KTX (Khronos Texture) Library and Tools. The toktx
CLI command is easiest. Or the other tools listed in the comments above.