[Python] mypy linter error (valid-type) with pydantic's Annotated pattern in a generic

Why would the following give a linter error in the second case but not the first:

# OK:
type MyAnnotatedType = Annotated[int | None, Field(strict=True)]
# Error: Invalid type alias: expression is not a valid type mypy(valid-type)
type MyAnnotatedSeqType = Sequence[Annotated[int | None, Field(strict=True)]]
# OK again:
type MyAnnotatedSeqTypeOK = Sequence[MyAnnotatedType]


Is this a limitation specified in PEP 593 somewhere, or more of a simplification in mypy to avoid more complex type inference, possibly requiring handling metadata at runtime?

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