APA 7 addresses appendices and supplemental materials in Section 2.14 and on page 41:

• The appendices follow the reference list.
• They are lettered "Appendix A," "Appendix B," "Appendix C," and so forth. If you have only one appendix, however, simply label it Appendix.
• Put figures and tables in separate appendices. The appendix title serves as the title for a table if it is the only table in the appendix.
• If you decide that certain figures and tables should appear in the same appendix, number them A1, A2, A3, and so forth, according to the appendix in which they appear.
• The materials in the appendix must not extend beyond the margins of the rest of the paper: Reduce the appendix materials as needed.

As a general guide, appendices are appropriate for any material that, if presented in the main body of the document, would unnecessarily interrupt the flow of the writing. Note that it is unlikely that you will use appendices in Walden course papers. For doctoral capstone studies, you might include some appendices with supplementary information.