Animation for object visibility and console error on layer context

Description

What is the preffered way to make an animation for something to be blinking but not a led.
So technically i want to make something visible and not visible.

Can it be done using the LV_OBJ_FLAG_HIDDEN to be add or clear?
Or to use the opacity

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

esp32, simulator

What LVGL version are you using?

8.3

What do you want to achieve?

Animation of a blinking object, shown/hidden/shown/hidden

What have you tried so far?

Tried to make an animation by using the add/clear flag but it did not work ,
i was trying to use the playback in order to revert the value but it did not do anything.

Is there any example that someone does flag control on animation?

I have also tried the opa which works fine but i get in console that i do not know what it is. Can someone help?

Code

void str_string_line_animator(ButtonTask animSelector,bool startAnim){

	lv_anim_t* anim;
	lv_obj_t* obj;

	switch (animSelector) {
		case MAINS:
			anim = &mainsAnim;
			obj=mainStrings;
			break;
		case CROSSES:
			anim = &crossesAnim;
			obj=crossStrings;
			break;
		default:
			break;
	}

	if(startAnim){
		lv_anim_init(anim);
		lv_anim_set_var(anim, obj);
		lv_anim_set_values(anim, LV_OPA_TRANSP, LV_OPA_COVER);
		lv_anim_set_time(anim, 500);
		lv_anim_set_playback_delay(anim, 500);
		lv_anim_set_playback_time(anim, 500);
		lv_anim_set_repeat_count(anim, LV_ANIM_REPEAT_INFINITE);

		lv_anim_set_exec_cb(anim, anim_flash);
		lv_anim_start(anim);

	}else{
		lv_anim_del(obj, anim_flash);
	}
}

static void anim_flash(void * var, int32_t v)
{
    lv_obj_set_style_opa(var, v, 0);
}

###  Console log.
[Warn]	(11.493, +36)	 lv_draw_sw_layer_create: Rendering this widget needs LV_COLOR_SCREEN_TRANSP 1 	(in lv_draw_sw_layer.c line #47)
[Warn]	(11.493, +0)	 refr_obj: Couldn't create a new layer context 	(in lv_refr.c line #909)

Warning fix is on lv_conf.h to set the variable as 1.