Why can’t I stop sharing notes

See -> hare notes on iCloud.com -> Share notes on iCloud.com – Apple Support (UK)

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Remove yourself from a shared note

If you are a participant, you can remove yourself from a shared note.

1. In Notes on iCloud.com, select the note you want to remove yourself from, then click .
2. Hold the pointer over your name, then click  and choose Remove Me.

Stop sharing notes

You must be the owner of a note to stop sharing it.

1. In Notes on iCloud.com, select the note you want to stop sharing in the notes list.
2. Click , then do one of the following:

• • Stop sharing with all participants: click Stop Sharing.
  • Stop sharing with just one participant: hold the pointer over the person’s name, then click  and choose Remove Access.