Hey there Sun_Goth,
Thanks for reaching out to the Apple Support Communities. To get started, are you going through the steps listed in following resource when trying to add a custom photo to your Shortcut icons: Add a shortcut to the Home Screen on iPhone or iPad - Apple Support
1. In the Shortcuts app on your iOS or iPadOS device, tap on a shortcut, then tap to open Details.
2. Tap Add to Home Screen.
3. Optional: To use a custom photo for a Home Screen icon, tap the icon (in the Home Screen Name and Icon area), then choose one of the following:
- Take Photo: Use the camera to take a new photo.
- Choose Photo: Select an existing photo from your Photos library.
- Choose File: Select a photo from the Files app.
4. Optional: To change the name that appears on the Home Screen, tap the name (in the Home Screen Name and Icon area), tap , enter a new name, then tap Return.
5. Tap Add.
The shortcut is added to your Home Screen.
If so, what happens when you try choosing a photo from your Camera Roll? For example, do you see any alerts or errors?
Have you tried restarting your iPhone since the issue started? If not, give that a try with the following steps: Restart your iPhone - Apple Support
How to restart your iPhone X, 11, 12, 13, or later
1. Press and hold either volume button and the side button until the power-off slider appears.
2. Drag the slider, then wait 30 seconds for your device to turn off. If your device is frozen or unresponsive, force restart your device.
3. To turn your device back on, press and hold the side button (on the right side of your iPhone) until you see the Apple logo.
While restarting may seem like a simple step, it can often help with resolving some unexpected issues like this.
Keep us updated on the results.
Take care!