What do you mean? How do I have to create a table with an IDENTITY KEY?

These defective by design functions incorrectly used by EclipseLink aren't related with column definitions in any way.

How do I have to create a table with an IDENTITY KEY?

There is no such thing as identity key in SQL (at least in the Standard and in H2), but there are identity columns and primary key columns. An identity column can (and usually should) have a primary key constraint and it can be defined with standard-compliant

CREATE TABLE TEST(
    ID BIGINT GENERATED BY DEFAULT AS IDENTITY PRIMARY KEY
);

https://h2database.com/html/grammar.html#column_definition

or with some legacy vendor-specific syntax (see documentation of compatibility modes).