Uploading screenshots not working

Welcome to the forum.

I already tried to cut it into the right form

Don't do so.

The way to do it is to use directly screen shots of the adapted simulator.

AppStoreConnect tells you what are the required sizes (other marked as optional).

You only have to provide 6.9" (or 6.7") for iPhone. Select the right simulator (such as 17 Pro max) and ctrl-S in the simulator. You will get the correct format.

You can provide more sizes optionnally.

I dont use Xcode. I Created the App with a third program. I cant use the Simulator, is there another way to do it?

You haven't actually clarified whether your screenshots are the right dimensions.

You've said:

I already tried to cut it into the right form for example 6,5" for the biggest screen.

What are the dimensions of the screenshots that App Store Connect is asking you for? A 6.9" iPhone 17 Pro Max, for example, should be 1320 x 2868. When you add those they will be resized by App Store Connect to fit all other iPhone sizes.

What are the dimensions of the screenshots you're trying to upload?

App Store Connect will tell you exactly what's wrong with your screenshots, so please copy that error message and paste it here (as text, not as an image, please).

You can use Preview app to resize the image at the exact dimension within resize in Tools menu.

I tried all the different Sizes. It says the Upload is not possible because its the wrong Size. Maybe its because I dont do it with xcode

Please tell what is the exact size of the image you try to load (read dimensions in image file information).

Is it a png image ?

Its 1240x2688 and I tried JPG and PNG