I’m trying to find a glTF file containing a KTX2 texture in these demos, in the list below…
…only one GLB is large enough to have a big texture, the 600KB one, and it doesn’t seem to use KTX2. I did see one loose .ktx2 texture loaded in the demo, as the lightmap – is that the texture you’re asking about, or should there be others?
When I was using ETC1S it was showing good results in terms of memory usage but textures were losing quality, so after searching about it I found out about UASTC and now quality is really good but having issues with memory.
If you have the full-resolution source textures available, sometimes using ETC1S at a larger resolution can still be a size and memory savings compared to JPEG or UASTC. ETC1S tends to be good best for color textures (e.g. base color) but not for normal maps. For normal maps you generally do need UASTC, or even PNG.
ETC1S will use less memory than UASTC as you mention, but I’m surprised that the UASTC version of your demo is using higher memory than JPEG… I think something else may be going on here and would like to look into that more.