Open files from Photo App with own app by using the Share Sheet

I want to open photos within the photo app with my app. My app already supports opening the file types public.png, public.jpeg, public.image

<key>CFBundleDocumentTypes</key>

	<array>

		<dict>

			<key>CFBundleTypeName</key>

			<string>My Files</string>

			<key>LSHandlerRank</key>

			<string>Alternate</string>

			<key>LSItemContentTypes</key>

			<array>

				<string>com.adobe.pdf</string>

				<string>public.png</string>

				<string>public.jpeg</string>

			</array>

		</dict>

	</array>

It works fine when a file of the given filetypes is opened in the Files App or as Attachment from Mail. If I click the share icon, my app appears in the Share Sheet. When selected, my app opens in full screen mode and is able to access the file. But when I select a Photo in the Photo app, my app does not appear as option in the share sheet.

Does anybody know why?

I am not interested in opening a Share Extension Sheet of my app. What I want is opening my app in full screen mode with the ability to access the shared file. I can see apps which are able to do exactly what I want. But I do not find any hints in the official docs.

Has anybody hints on how I can achieve this?