Hello Irgcecilia.
Thanks for reaching out to Apple Support Communities. We understand that your Notes app is not working properly. We will be glad to assist.
To get started, let's ensure that you've set up Notes with iCloud as follows:
Use Notes on your iPhone, iPad, and iPod touch
You can use iCloud to update your notes across all of your devices. To set up Notes with iCloud, go to Settings > [your name] > iCloud, then turn on Notes. You’ll see your notes on all of your Apple devices that you’re signed in to with the same Apple ID."
If there's no change after, let's close the Notes app then restart your to see if that helps.
Close an app on your iPhone or iPod touch
Restart your iPhone
If you need more help, Contact Apple for support and service
Cheers.