In the current implementation, we use "script" destination for module loading for PaintWorklet:
https://chromium.googlesource.com/chromium/src/+/8dab5ecef922e12366bfd749d6a3f2d5e5e57c1b/third_party/blink/renderer/core/workers/worklet_global_scope.cc#104

According to the Fetch spec, this should be "paintworklet" destination:
https://fetch.spec.whatwg.org/#concept-request-destination

Note that the destination should be specified by the PaintWorklet spec, but currently the base Worklet spec doesn't provide a way to override the destination. I filed a spec issue about it:
https://github.com/w3c/css-houdini-drafts/issues/759

See also  issue 842566  for details. This issue was split from there.