You are viewing version 6.0.0 of the library, the latest version is
<!-- Material unchecked -->
<div class="form-check ">
    <input type="radio" class="form-check-input" id="materialUnchecked" name="materialExampleRadios">
    <label class="form-check-label" for="materialUnchecked">Material unchecked</label>
</div>

<!-- Material checked -->
<div class="form-check ">
    <input type="radio" class="form-check-input" id="materialChecked" name="materialExampleRadios" checked>
    <label class="form-check-label" for="materialChecked">Material checked</label>
</div>

Radio button

Base on the version from MDB:
https://mdbootstrap.com/jquery/forms/radio-button/

A ‘radio button’ is a component used to allow a user to make a single choice among a number of options (whereas Checkboxes are used for selecting multiple options).