How to make my UI transperent

Description

I’m useing LVGL 9 to create a UI on a linux drm plane.
UI itself works for me.
I have gstreamer playing a video on the overlay plane and want to use LVGL to draw the UI over the video.

What MCU/Processor/Board and compiler are you using?

Radxa Zero 3W

What LVGL version are you using?

9-master

What do you want to achieve?

I need the UI to be transperent where nothing is drawn (black background)

What have you tried so far?

Changed the color format to be #define DRM_FOURCC DRM_FORMAT_ARGB8888
When useing modetest to set the alpha of the plane this affects all colors.

Code to reproduce

I run the a basic hello world menu.

The code block(s) should be formatted like:

int main(int argc, char **argv)
{
    // setup keybard inout from stdin
    set_stdin_nonblock();
    printf("WASD Navigation active (Q to quit)\n");

    /* Initialize LVGL. */
    lv_init();

    /* Initialize libDRM */
    const char *device = "/dev/dri/card0";
    lv_display_t * disp = lv_linux_drm_create();

    lv_linux_drm_set_file(disp, device, -1);

    // Create a virtual keyboard input device
    lv_indev_t * kb_indev = create_virtual_keyboard();

    // Check if the virtual keyboard was created successfully
    if (kb_indev) {
        printf("Virtual keyboard created successfully!\n");
    } else {
        printf("Error: Could not create virtual keyboard!\n");
    }

    /*Change the active screen's background color*/
    lv_obj_set_style_bg_color(lv_screen_active(), lv_color_hex(0x000000), LV_PART_MAIN);

    /*Create a white label, set its text and align it to the center*/
    lv_obj_t * label = lv_label_create(lv_screen_active());
    lv_label_set_text(label, "Hello world");
    lv_obj_set_style_text_color(lv_screen_active(), lv_color_hex(0xffffff), LV_PART_MAIN);
    lv_obj_align(label, LV_ALIGN_CENTER, 0, 0);

    while (1) {

        // Handle keyboard input
        handle_keyboard_input();

        lv_task_handler();
        //ui_tick();
        usleep(5000);  // Sleep for a short period to allow LVGL to update
    }

    //lv_linux_run_loop();
    //sleep(50);

    return 0;
}

changes in lv_conf.h

#define LV_COLOR_DEPTH 32
#define LV_USE_LINUX_DRM        1
#define LV_USE_EVDEV    1

Meanwhile i found this in the documentation: is Widget Basics — LVGL documentation

However setting this does not change anything.

Narrowed it down further:

This gives me a transperent label:

lv_obj_t * label = lv_label_create(lv_screen_active());

While this gives me a non transparent rectangle:

lv_obj_t *obj = lv_obj_create(lv_screen_active());

I have to add

lv_obj_set_style_opa(obj, 0, LV_PART_MAIN | LV_STATE_DEFAULT);

to make the rectangle transparant.
However when doing this in EEZ-Studio this does not work.