How to turn off HTML input form field suggestions?

What you want is to disable HTML autocomplete Attribute.

Setting autocomplete=”off” here has two effects:

It stops the browser from saving field data for later autocompletion
on similar forms though heuristics that vary by browser. It stops the
browser from caching form data in session history. When form data is
cached in session history, the information filled in by the user will
be visible after the user has submitted the form and clicked on the
Back button to go back to the original form page.

Read more on MDN Network

Here’s an example how to do it.

<form action="#" autocomplete="on">
  First name:<input type="text" name="fname"><br> 
  Last name: <input type="text" name="lname"><br> 
  E-mail: <input type="email" name="email" autocomplete="off"><br>
  <input type="submit">
</form>

If it’s on React framework then use as follows:

<input
    id={field.name}
    className="form-control"
    type="text"
    placeholder={field.name}
    autoComplete="off"
    {...fields}/>

Link to react docs

Update

Here’s an update to fix some browsers skipping “autocomplete=off” flag.

<form action="#" autocomplete="off">
  First name: <input type="text" name="fname" autocomplete="off" readonly onfocus="this.removeAttribute('readonly');"><br> Last name: <input type="text" name="lname" autocomplete="off" readonly onfocus="this.removeAttribute('readonly');"><br> E-mail:
  <input type="email" name="email" autocomplete="off" readonly onfocus="this.removeAttribute('readonly');"><br>
  <input type="submit">
</form>