Use the correct markup for the Bootstrap modal, and add the appropriate trigger to your button.
<button type="button" class="btn btn-lg btn-primary" data-toggle="modal" data-target="#myModal">POC</button>
...
<div class="modal-body">
<!--
<a class="btn btn-primary dropdown-toggle mr-4" type="button" data-toggle="dropdown" aria-haspopup="true"
aria-expanded="false">Basic dropdown</a>
<div class="dropdown-menu">
<a class="dropdown-item" href="#">Action</a>
<a class="dropdown-item" href="#">Another action</a>
<a class="dropdown-item" href="#">Something else here</a>
<div class="dropdown-divider"></div>
<a class="dropdown-item" href="#">Separated link</a>
</div>
<div class="custom-control custom-checkbox">
<input type="checkbox" class="custom-control-input" id="defaultChecked2" checked>
<label class="custom-control-label" for="defaultChecked2">Default checked</label>
</div>
</div>
...
Demo[
^]
Modal · Bootstrap v4.6[
^]