Search for graphics and photos around a theme or colour scheme from your personal photos and on Pinterest, Instagram, and Google Images. If you want to go with a seasonal look, check out these Halloween aesthetic inspo pictures.
You can use the free Procreate Pocket app to create artistic (or solid colour) backgrounds and icon images for your home screen.
The free and easy-to-use Canva app is great for designing social graphics, icons, and wallpapers.
I used the A Design Kit app to design all the graphics you see here. It's a user-friendly app that I personally love for creating artistic designs that combine art and text.