items is not valid as per draft2020 but is valid for draft2019. Now it fails because the whole JSON is validated against draft2020 meta-schema + embedded schemas individually. This is not a valid behavior according to specification (https://json-schema.org/draft/2020-12/json-schema-core#name-validating).
Let's consider a multi-spec (compound) schema:
items
is not valid as per draft2020 but is valid for draft2019. Now it fails because the whole JSON is validated against draft2020 meta-schema + embedded schemas individually. This is not a valid behavior according to specification (https://json-schema.org/draft/2020-12/json-schema-core#name-validating).