I have some trouble using mkdocs because I run into this error using WinPython:
https://squidfunk.github.io/mkdocs-material/plugins/requirements/image-processing/#troubleshooting
Problem seems to be cairocffi not finding the cairo library.

After some investigation I found that the cairo library is present at %WINPYDIR%\Lib\site-packages\wx.

Furthermore I found out that cairocffi supports an environment variable CAIROCFFI_DLL_DIRECTORIES.
I thought setting this in env.bat would fix the problem but it did not. I added it to PATH as well. This did work.

...
:after_pyzo_conf


rem ******************
rem handle cairocffi / wx if included
rem ******************
set tmp_pyz=%WINPYDIR%\Lib\site-packages\wx
if not exist "%tmp_pyz%" goto end_wx_conf
set CAIROCFFI_DLL_DIRECTORIES=%WINPYDIR%\Lib\site-packages\wx
set "PATH=%WINPYDIR%\Lib\site-packages\wx;%PATH%;"
:end_wx_conf


set tmp_pyz


rem ******************
rem WinPython.ini part (removed from nsis)
rem ******************
...