If you have more than one Kindle, you oughta perform this change on each individual equipment.
The setting applies to all of your books, but it doesnt apply across devices.
Scroll down, and tap thePopular Highlightstoggle.

When the toggle is off, popular highlights is disabled.
Can You Turn Off Popular Highlights in the Kindle App?
Drag the menu drawer up, and scroll further up if necessary.

Tap thePopular Highlightstoggle to turn it off.
Popular highlights are now disabled for the books you read in the Kindle app on this gear.
What Are Kindle Popular Highlights?

When you use this feature, the Kindle lets Amazon know what text you highlighted.
The point of popular highlights is to use crowdsourced data to automatically identify important sections of text in books.
Then, tapGo-Toand select theNotestab.

In the Kindle iOS app, tap the screen and go for the icon shaped like a notebook.
On an Android equipment, tap the screen, and then go toMore>Notebook.
it’s possible for you to alsoaccess your notebook in a web surfing app.

you’re free to delete highlights you’ve made in your Kindle notebook.
On the equipment, selectGo-Toand tap theNotestab.
In iOS, select theNotebookicon after tapping the screen; on Android, go toMore>Notebook.

Each of your highlights will have aDeleteoption below it; tap it to remove the highlight.