Salutations drd1957,
Making changes to an existing note should be an option, but let’s explore some things that may be impacting the Notes app.
Your profile says we’re working with an iPhone 6 running iOS 12. iOS 12.5.6 is the latest that device can update to. Do you sync your notes with any services, such as iCloud? If you’re using iCloud, do you also access those notes on any devices that are running more recent versions of macOS, iPadOS or iOS such as iOS/iPadOS 16 or macOS Ventura?
A few basic steps we can also work through -
• Force quite and relaunch the Notes app Close an app on your iPhone or iPod touch
• Restart your iPhone Restart your iPhone
• Create a new note and try to edit that one, to see if the issue is specific to pre-existing notes Use Notes on your iPhone, iPad, and iPod touch
Create a new note
1. Open Notes.
2. Tap the Compose button, then create your note.
3. Tap Done.
The first line of the note becomes its title. To change the formatting style of the first line, go to Settings > Notes > New Notes Start With, then select an option.
You can also quickly access Notes from Control Center. Go to Settings > Control Center, and add Notes. Then open Control Center and tap Notes to create a note. Or, just ask Siri to "Start a new note."
Thanks.