Bootstrap 4: Dropdown menu is going off to the right of the screen

In Bootstrap 5 (beta 2) you can use dropdown-menu-end:

<div class="dropdown-menu dropdown-menu-end">
  ...
</div>

Bootstrap has this built in already: See Menu Alignment. Just add the dropdown-menu-right class to the dropdown-menu div.

<div class="dropdown-menu dropdown-menu-right">

Working Example: (open Full Page)

<link href="https://cdnjs.cloudflare.com/ajax/libs/twitter-bootstrap/4.5.0/css/bootstrap.min.css" rel="stylesheet" />
<nav class="navbar navbar-expand-xl navbar-dark bg-primary">

  <button class="navbar-toggler" type="button" data-toggle="collapse" data-target="#navbarSupportedContent" aria-controls="navbarSupportedContent" aria-expanded="false" aria-label="Toggle navigation">
        <span class="navbar-toggler-icon"></span>
    </button>

  <a class="navbar-brand" href="#">Company</a>

  <div class="collapse navbar-collapse" id="navbarSupportedContent">
    <form action="#" class="form-inline my-2 my-lg-0">
      <input class="form-control mr-sm-2" id="keyword" name="keyword" :value='keyword' type="text" placeholder="Search for jobs" />
      <input class="form-control mr-sm-2" id="location" name="location" :value='location' type="text" placeholder="Location" />
      <button class="btn btn-secondary my-2 my-sm-0" type="submit">Find Jobs</button>
    </form>

    <ul class="navbar-nav mr-auto">
      <li class="nav-item">
        <a href="#" class="nav-link active">
          <strong>Post Job</strong>
        </a>
      </li>
      <li class="nav-item">
        <a href="#" class="nav-link">
          <strong>Register</strong>
        </a>
      </li>
      <li class="nav-item">
        <a href="#" class="nav-link">
          <strong>Profile</strong>
        </a>
      </li>
      <li class="nav-item">
        <a href="#" class="nav-link">
          <strong>My Jobs</strong>
        </a>
      </li>
      <li class="nav-item">
        <a href="#" class="nav-link">
          <strong>My Searches</strong>
        </a>
      </li>
      <li class="nav-item">
        <a href="#" class="nav-link">
          <strong>Employer Dashboard</strong>
        </a>
      </li>
      <li class="nav-item">
        <a href="#" class="nav-link">
          <strong>Login</strong>
        </a>
      </li>
      <li class="nav-item">
        <a href="#" class="nav-link">
          <strong>Logout</strong>
        </a>
      </li>
    </ul>

    <ul class="navbar-nav">
      <li class="nav-item dropdown">
        <a class="nav-link dropdown-toggle" href="#" id="navbarDropdown" role="button" data-toggle="dropdown" aria-haspopup="true" aria-expanded="false">
          <strong>Account</strong>
        </a>
        <div class="dropdown-menu dropdown-menu-right" aria-labelledby="navbarDropdown">
          <a class="dropdown-item">
            <strong>Register</strong>
          </a>
          <a href="#" class="dropdown-item">
            <strong>Profile</strong>
          </a>
          <a href="#" class="dropdown-item">
            <strong>My Jobs</strong>
          </a>
          <a href="#" class="dropdown-item">
            <strong>My Searches</strong>
          </a>
          <a href="#" class="dropdown-item">
            <strong>Employer Dashboard</strong>
          </a>
          <a href="#" class="dropdown-item">
            <strong>Login</strong>
          </a>
          <a href="#" class="dropdown-item">
            <div class="dropdown-divider"></div>
            <strong>Logout</strong>
          </a>
        </div>
      </li>
    </ul>
  </div>
</nav>

<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.5.1/jquery.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/popper.js/2.4.2/umd/popper.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/twitter-bootstrap/4.5.0/js/bootstrap.min.js"></script>