I have been looking at everything but cannot find a single tool that can take an HDR file and convert it to a RGBA 16bit cubemap in KTX. Or a tool that can convert DDS cubemap to KTX?
The cubemap filtering tool can do that: GitHub - dariomanesku/cmft: Cross-platform open-source command-line cubemap filtering tool.</title
It’s a bit dated though, so it can only convert to KTX1.
I end up using glTF IBL Sampler, which was able to export to KTX2 and had a guide on how to use the tool.