This is most likely a software bug, not normal behavior or user error. Artifacts like isolated bright “sparkles” often happen when an image-processing step produces values outside the range the code expects, then those values get clipped or wrapped because of a data-type problem such as integer overflow/underflow or incorrect handling of unsigned values. Since the artifacts also appear in exports, they’re being baked into the processed image rather than just showing in preview. In short: if a darktable module creates hot-pixel-like specks at certain settings, that strongly suggests a bug in that module’s calculations rather than anything specific to your Canon RAW files.