What does standard SQL or any of the non-PostgreSQL SQLs do instead of RETURNING?
The Standard SQL Way™ of generating IDs is to


create a sequence for the table;
read the next value with SELECT NEXT VALUE FOR seq_name¹; and then
insert a complete row, including the ID value.


Before SQL:2003, there were no autogenerated IDs. And in SQL:2003, there appears to be no method to read the last GENERATED AS IDENTITY value.

¹ Postgres does not support this, and requires SELECT nextval('seq_name').