As noted in the release email, linked to from the release tweet and noted in large orange warning that appears on the front page of the documentation, and less orange, but still present, in the readme on the repository and the release on pypi:
xlrd has explicitly removed support for anything other than xls files.
In your case, the solution is to:
openpyxl: https://openpyxl.readthedocs.io/en/stable/df1 = pd.read_excel(
os.path.join(APP_PATH, "Data", "aug_latest.xlsm"),
engine='openpyxl',
)