I have this function to render some simple boxes:

    public static void drawLineBox(PoseStack matrixStack, AABB aabb, float r, float g, float b, float a) {
        Entity camEntity = MC.getCameraEntity();
        double d0 = camEntity.getX();
        double d1 = camEntity.getY() + camEntity.getEyeHeight();
        double d2 = camEntity.getZ();
 
        RenderSystem.disableDepthTest(); // enable showing lines through blocks
        RenderSystem.depthMask(false);
 
        VertexConsumer vertexConsumer = MC.renderBuffers().bufferSource().getBuffer(RenderType.lines());
 
        matrixStack.pushPose();
        matrixStack.translate(-d0, -d1, -d2); // because we start at 0,0,0 relative to camera
        LevelRenderer.renderLineBox(matrixStack, vertexConsumer, aabb, r, g, b, a);
        matrixStack.popPose();
    }

But these though i've disabled the depth test and depthMask the lines still won't show through blocks. I'm running the above inside RenderLevelStageEvent with the stage set to RenderLevelStageEvent.Stage.AFTER_TRANSLUCENT_BLOCKS (I've also tried AFTER_SOLID_BLOCKS).

I've also tried moving around the disable lines to after the pushPose() but that's not worked either...

I'm no expert on this stuff.

But this simple test based on your code works for me (render a box 10 blocks below the player)

@EventBusSubscriber(modid = MODID, value = Dist.CLIENT)
public class RenderTest {

    public static void drawLineBox(PoseStack matrixStack, AABB aabb, float r, float g, float b, float a) {
        RenderSystem.disableDepthTest();
        VertexConsumer vertexConsumer = Minecraft.getInstance().renderBuffers().bufferSource().getBuffer(RenderType.lines());
        LevelRenderer.renderLineBox(matrixStack, vertexConsumer, aabb, r, g, b, a);
        RenderSystem.enableDepthTest();
    }

    @SubscribeEvent
    public static void renderTest(RenderLevelStageEvent event) {
        if (event.getStage() == RenderLevelStageEvent.Stage.AFTER_TRIPWIRE_BLOCKS) {
            AABB shape = Shapes.block().bounds().move(0, -10, 0);
            drawLineBox(event.getPoseStack(), shape, 1.0f, 1.0f, 1.0f, 1.0f);
        }
    }
}

The box is offset in F5/third person mode towards the camera so there's obviously some additional calculation needed for that? Like I said, no expert.

Oh I found the issue, for some reason this only works while NOT in spectator mode, but unfortunately my mod requires you to be in spectator mode most of the time...

I've tried with all stages, and it seems spectator mode just hard-sets the depth test on or something like that.

If anyone knows where this is actually done, I could maybe modify it with a mixin or access transformer...