Are there any command-line tools or python APIs which can help to check multiple Word and PowerPoint documents for accessibility issues automatically/programmatically?
For command-line tools, you can try using:

LibreOffice CLI: LibreOffice provides a Command Line Interface (CLI) tool that can be used to perform various document operations, including checking for accessibility issues.

For Python APIs, you can try using:

python-docx: A library for working with Microsoft Word (.docx) files. It allows you to extract the text from a Word document and check it for accessibility issues.

python-pptx: A library for working with Microsoft PowerPoint (.pptx) files. It allows you to extract the text and images from a PowerPoint presentation and check them for accessibility issues.

accessibility-checker: A Python library that uses the Microsoft Office UI Automation API to check documents for accessibility issues.
Checking accessibility issues for Word and PPT files from command-line