No images in the mobile app

I am a beginner and I follow some yt videos for building my first app. The problem is that in the mobile app (Android 11) the images are not displayed like in the web app. I only see emtpy image placeholders, but an additional output of the path to the images shows that the url paths are correct.

  <ion-avatar slot="start">
    <img [src]="imageBaseUrl + '/' + item.poster_path">

I started the project with:
$ ionic start movieapp blank --type=angular --capacitor

and to see the app on my smartphone I use
$ ionic cap run android -l --external

I see the images in the browser when I start the app with
$ ionic serve

Do you already have an idea of the problem or do you need further information?

I could fix the problem myself, but I dont know the exact reason. First I changed the img-Tag to ion-img (I saw it in your first photo-gallery app). Then I called the commands $ ionic build and $ ionic cap copy and then $ ionic cap run android -l --external. Now I can see the images on my smartphone too.