I have been using version 5.3 (and it has the same issue).
If in hibernate config file, in version 5.3, I put an space after the 'hibernate.hbm2ddl.auto' value, e.g. 'create ' it throws an exception: IllegalArgumentException: "Unrecognized legacy `hibernate.hbm2ddl.auto` value : create).

I saw that in the master version, it was resolved with a trim():
https://github.com/hibernate/hibernate-orm/blob/master/hibernate-core/src/main/java/org/hibernate/tool/schema/Action.java line 153

But, if I try to use a property to generate schema files within the hibernate property config:
javax.persistence.schema-generation.scripts.action and the value has a space: 'drop-and-create ', it keeps throwing the exception.

The solution is very simple: add also a trim() in line 104 for interpretJpaSetting function , not only to interpretHbm2ddlSetting function :
final String name = value.toString().trim();