Z fighting in grease pencil by angle

You don't really have z-fighting in grease pencil unless you are using multiple GP objects. I would separate the fills from the lines in a separate layer. So since I don't know your setup I'm going to give some general guidance. If they are multiple object then just move the objects slightly in the 3D space. For example: select the object you want to move and press G->The axis you want to move->type something like 0.002 or -0.002. If they are separate layers then reorder the layer. Goto the layers panel and select layer and press up or down button on the right. This panel can be found in the top of the header or the properties editor->Data/Grease Pencil tab. If they are in the same layer then you can select the GP and press tab to enter edit mode. Select the fill or line(Select a control point/vertex and press L or switch to stroke selection by pressing 2 on top row.) Then you can move the order by using Ctrl+arrow up/down or you can move to a new/different layer by pressing M. 

If it is because of Z Fighting, because what it causes is the fill of the object and both the fill and the line are on different layers.

This is the latest version of Blender, Blender 4.4

Oh, I didn't know, well maybe I'll update it later.

For now, I want to know how to fix the Z fighting the fill with the line. Just knowing is more than enough for me for now.

You will need go into edit mode select the fills or the strokes. Then Press shift+Ctrl+ either up arrow key or down arrow key. Depending on which you selected. You can also access thru the menu Stroke->Arrange-> and then either Send to back or Bring to front. You will also want the stroke depth order set to 2D layers. I haven't used the 3D Location setting so I'm not familiar with it. I had to look up what the default setting is and it's 2D Layers.

I've tried that, but it doesn't work for what I'm trying to do.

Moving a line forward or backward with Shift + Control plus the arrow works if the fill and the line are on the same layer, but it still doesn't fix the lines.

The only other option I can think of is to move the pieces in the 3D space, which can be done in edit mode.