transfer photos from I phone to desk top, how?

You'll have to use the Windows Photo App, check this:

...

Import to your Windows PC

You can import photos to your PC by connecting your device to your computer and using the Windows Photos app:

1. Make sure that you have the latest version of iTunes on your PC. Importing photos to your PC requires iTunes 12.5.1 or later.
2. Connect your iPhone, iPad, or iPod touch to your PC with a USB cable.
3. If asked, unlock your iOS or iPadOS device using your passcode.
4. If you see a prompt on your iOS or iPadOS device asking you to Trust This Computer, tap Trust or Allow to continue.

Then, visit Microsoft's website to learn how to import photos to the Windows Photos app in Windows 10.

If you have iCloud Photos turned on, you need to download the original, full resolution versions of your photos to your iPhone before you import to your PC. Find out how.

When you import videos from your iOS or iPadOS device to your PC, some might be rotated incorrectly in the Windows Photos app. You can add these videos to iTunes to play them in the correct orientation.

If you're having trouble importing photos from your iOS or iPadOS device to Windows 10, try these steps:

1. On your iOS or iPadOS device, open the Settings app. Tap Camera, then tap Formats.
2. Tap Most Compatible. From now on, your camera will create photos and videos in JPEG and H.264 formats.

Learn what to do if you can't import photos from your iPhone, iPad, or iPod touch to your computer.

...

copied from: Transfer photos and videos from your iPhone, iPad, or iPod touch - Apple Support

Fotos und Videos von deinem iPhone, iPad oder iPod touch übertragen - Apple Support (DE)

If you want to transfer the photos to your PC, follow the steps mentioned above, using the Windows Photo App.

On a Mac, follow these steps:

...

Import to your Mac

You can use the Photos app to import photos from your iPhone, iPad, or iPod touch to your Mac.

1. Connect your iPhone, iPad, or iPod touch to your Mac with a USB cable.
2. Open the Photos app on your computer.
3. The Photos app shows an Import screen with all the photos and videos that are on your connected device. If the Import screen doesn't automatically appear, click the device's name in the Photos sidebar.
4. If asked, unlock your iOS or iPadOS device using your passcode. If you see a prompt on your iOS or iPadOS device asking you to Trust This Computer, tap Trust to continue.
5. Choose where you want to import your photos. Next to "Import to," you can choose an existing album or create a new one.
6. Select the photos you want to import and click Import Selected, or click Import All New Photos.
7. 
8. 
   
9. Wait for the process to finish, then disconnect your device from your Mac.

Learn what to do if you can't import photos from your iPhone, iPad, or iPod touch to your computer.

...

copied from: Transfer photos and videos from your iPhone, iPad, or iPod touch - Apple Support

Thanks for posting your question in the Apple Support Communities. 

We have a Community for English speakers here: Official Apple Support Community

Please feel free to join and post your question there, or repost your question in German here: Offizielle Apple Support-Community