In general, H5P-based interactive materials are not accessible. Whether they are used as part of a textbook or in an ADAPT homework question, you should be wary of their usefulness. ADAPT has many native question types that are built to be accessible and can be used embedded in textbooks, as well.
However, since many people use H5P, we have built a guide on H5P Accessibility, including a chart that breaks down which activities in H5P are accessible.
ADAPT does have tools for creating alternate questions for any activity which can be automatically provided to students who are listed as needing alternative accessible options. Check the full ADA accessibility document here. Also: check out the instructions for how to create an accessible alternate question in ADAPT and other accessibility details in LibreTexts in our presentation at LibreFest.