I don’t understand your first question, the initialization of the WebGPU engine does not affect how the texture sampling will be done. Does your project work in WebGL? I think we would need a repro in the Playground or a link to your project to be able to help more. Also, try to use a newer version (we are currently at 5.10.0), maybe something has been corrected on the WebGPU side since 5.2.0.
Regarding your 2nd question, WebGPU does not support bilinear filtering of 32 bits float textures yet (an extension should add this support in the future). You should try with a 16 bits float texture instead (TEXTURETYPE_HALF_FLOAT) where bilinear filtering is supported out of the box.