Do oxf.jar and oxfInstMock.jar support Java 21?

Answer

oxf.jar and oxfInstMock.jar are considered as the "Redistributables".

IBM provides the "Redistributables" without obligation of support and "AS IS".

See the following license document of Rhapsody for details.

IBM Rhapsody 9.0.2 GA - "IBM International Program License Agreement"
https://www.ibm.com/support/customer/csol/terms/?id=L-KBAL-AKTZ4A&lc=en
 

Redistributables

The Program includes components that are Redistributable and they are listed below. Redistributables may be distributed, in object-code form, only as part of Licensee's value-added application that was developed using the Program ("Licensee's Application") and only to support use of Licensee's Application. If the Redistributables include a Java Runtime Environment, Licensee must also include other non-Java Redistributables with Licensee's Application. Licensee may not remove any copyright or notice files contained in the Redistributables or use IBM's, it's suppliers' or distributors' names or trademarks in connection with the marketing of Licensee's Application without IBM's or that supplier's or distributor's prior written consent. Licensee's license agreement with the end user must be at least as protective of IBM as the terms of this Agreement.

IBM, its suppliers and distributors provide the Redistributables and related documentation without obligation of support and "AS IS", WITH NO WARRANTY OF ANY KIND, EITHER EXPRESS OR IMPLIED, INCLUDING THE WARRANTY OF TITLE, NON-INFRINGEMENT OR NON-INTERFERENCE AND THE IMPLIED WARRANTIES AND CONDITIONS OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. 

The following are Redistributables:
Engineering Rhapsody Redistributables

The following lists include files that are provided to you pursuant to the Redistributables section of the IBM International Program License Agreement's License Information that applies to this Program:

All source files in one of the following directories (or subdirectories of these directories) may be compiled and redistributed in object form only: 
 - \Share\LangAda
 - \Share\LangAda83
 - \Share\LangAda95
 
All source files in the following directories (or subdirectories of these directories) may be compiled and redistributed in object form only: 
 
 - \Share\LangC\
 - \Share\LangCpp\
 - \Share\WebServices\
 
All .java files in the following directories (or subdirectories of these directories) may be compiled and redistributed in class form only: 

 - \Share\LangJava\src\


All .jar, .lib, .dll files in the following directory may be redistributed:
 
 - \Share\LangJava\lib\
 

\Share\JavaAPI\rhapsody.jar may be redistributed.