Define requirements using setuptools-declarative-requirements package
MODIFY
pyproject.toml
pyproject.toml
[build-system]
requires = [
+ "setuptools-declarative-requirements",
"setuptools>=42",
"wheel",
]

MODIFY
setup.cfg
setup.cfg
@@ -32,3 +32,9 @@ exclude =
[options.entry_points]
console_scripts =
plex-trakt-sync = plex_trakt_sync.cli:cli
+
+[requirements-files]
+# setuptools does not support "file:", so use a extra package for this:
+# https://pypi.org/project/setuptools-declarative-requirements/
+# https://github.com/pypa/setuptools/issues/1951#issuecomment-718094135
+install_requires = requirements.txt

Define requirements using setuptools-declarative-requirements package