Hey there DorisJode,
With regards to turning off two-factor authentication, we recommend using the info below for clarification:
If you already use two-factor authentication, you can no longer turn it off. Certain features in the latest versions of iOS and macOS require this extra level of security, which is designed to protect your information. If you recently updated your account, you can unenroll within two weeks of enrollment. Just open your enrollment confirmation email and click the link to return to your previous security settings. Keep in mind, this makes your account less secure and means that you can't use features that require higher security.
Two-factor authentication for Apple ID - Apple Support
If you're still running into the loop with the questions, try closing the app you're using, restart your iPhone, and check again. Should it persist, make sure you have the latest OS version on your device to help if this is software related.
Feel free to reply with more details if you need additional help.
Take care!