I have a CFD solver that works with a quadtree mesh. However, I’m unable to create a VTU file because I can’t understand what the offsets array means? Can someone tell me how to create the offsets array? What distance is that?

Also I’d like to know if paraview does not take into account the order of the nodes in the connectivity list? Because, no matter the order I put them in my file, paraview would join them in an ascending order. Is there any way to ask paraview to join them in the same order that the nodes are given?

You may want to ask this question on the VTK discourse.
https://discourse.vtk.org/

In any case, here are the VTK formats specifications.
https://vtk.org/wp-content/uploads/2015/04/file-formats.pdf

Array offsets are mentioned page 15.