Hello,
If you have tried to run a calculation with the plugin, the model should have been created under:
%USERPROFILE%\AppData\Roaming\QGIS\QGIS3\profiles\default\python\plugins\Mascaret\mascaret
There is a ".lis" file that contains the output information from the software.
You can also run the model with the standalone executable to see if there is more information.
Of course, it is possible to use the Python APIs, but for that, you will need to install Open Telemac-mascaret. You will find an Python APIs example under \examples\python3\TelApy_api or examples\python3\telapy_study\mascaret
But without a specific error, it is difficult to answer your question.