Hi Léa,
As we have seen you were using Guttenberg to edit the pages. However, this theme still not support Guttenberg. In this issue, you need to use Classic Editor that we already installed on your WordPress.
Moreover, the about section may have an issue. You need to create the section from the Section Creators. After then you will get them in the sections tab of the page. Please watch this video tutorial about “How to Create A Section and Setup the Section in A Page on CVIT” https://www.youtube.com/watch?v=v0Si7axXXUM&index=6&t=0s&list=PLbmIKrgYlRbq9I5C4_GZN7yBCGgddhprP
We have listed the issue in our theme update list to fix the issue in our next update of the theme.
Best Regards,
ThemeLooks Support Team