I'm new using QGIS (version 3.22) and I think my doubt is simple, but I didn't find any answer.
I have a vector shapefile from Brazil like this: https://geoftp.ibge.gov.br/organizacao_do_territorio/malhas_territoriais/malhas_municipais/municipio_2020/Brasil/BR/BR_UF_2020.zip.
And I have another shapefile with a contour like one of these: https://dados.ons.org.br/dataset/bacia_contorno.
I want to use the contour to crop a piece of the shapefile and get the points inside. What I want to do is cut like a "biscuit mold".
I tried use Vector > Geometry Tool > Clip or Intersection... but the contour is empty inside and result the same contour but not filled inside.