now trying to read vueuse codes.
2 type arg Ref can be seen in exported types by running pnpm run build:types
e.g:
types/packages/core/useDeviceMotion/index.d.ts

Ref<DeviceMotionEventAcceleration | null, DeviceMotionEventAcceleration | null>

deepRef(alias of ref) returning 2-type-arg-Ref even though normal annotation exists.

I guess my understanding was wrong.
Ref was modified to receive 2 type args on this PR in vuejs/core (v3.5). (not v3.4.35 cuz Evan reverted it in minor branch.)

vueuse v11.2 builds d.ts files as vue ^3.5.12 and my project was using vue 3.4.38.
Currently vueuse specifies the vue version as peerDependencies, so it probably doesn't have the same problem.