Try it

pip3 install mkdocs
pip3 install pymdown-extensions
mkdocs serve

Try with patched mkdocs

Install regular version first

pip3 install mkdocs
pip3 install pymdown-extensions

Install the patched version 'somewhere'

cd /some/path
git clone https://github.com/dersimn/mkdocs
cd mkdocs
pip3 install -e .

Clone this demo repository

cd /some/other/path
git clone https://github.com/dersimn/mkdocs-snippets-issue
cd mkdocs-snippets-issue

Now hotwire the patched version:

export PYTHONPATH="/some/path/mkdocs"

Build and serve

mkdocs serve

Browse to http://localhost:8000.