nowosad, Have you ever got a spatial object with broken geometry (e.g., an invalid polygon)? Do you want to learn about this topic and also learn how to fix it?
There is a great repo and shiny app created by defuneste.
You can find it at https://github.com/defuneste/utile_comme_du_pq.
A list of tools for geometry correction
A shiny app explaining geometry correction
An explanation of a valid polygon