Bootstrap is a free framework that is used to create responsive websites using a mobile-first strategy more quickly and easily. It is open-sourced framework. Colors in Bootstrap 4 are restricted.

Custom form controls are included in Bootstrap 5. The form controls in Bootstrap 4 used whatever presets each browser offered. Because of its bespoke design, the form controls in Bootstrap 5 will have a much more uniform appearance and feel across all browsers.

From that point forward, no new features will be added to Bootstrap 4. Bug fixes, security updates, and content updates will continue to be applied.

Comparison

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# Explanation
The following code will show a form that will take username and password, then a submit button will submit the form. The description of form is written in the paragraph. The code goes for Bootstrap 4 and Bootstrap 5 altogether.

<!DOCTYPE html>
<html>
   <head>
      <link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/4.0.0/css/bootstrap.min.css" integrity="sha384-Gn5384xqQ1aoWXA+058RXPxPg6fy4IWvTNh0E263XmFcJlSAwiGgFAW/dAiS6JXm" crossorigin="anonymous">
      <link href="https://cdn.jsdelivr.net/npm/bootstrap@5.0.2/dist/css/bootstrap.min.css" rel="stylesheet" integrity="sha384-EVSTQN3/azprG1Anm3QDgpJLIm9Nao0Yz1ztcQTwFspd3yD65VohhpuuCOmLASjC" crossorigin="anonymous">
   </head>
   <body>
      <script src="https://code.jquery.com/jquery-3.2.1.slim.min.js" integrity="sha384-KJ3o2DKtIkvYIK3UENzmM7KCkRr/rE9/Qpg6aAZGJwFDMVNA/GpGFF93hXpG5KkN" crossorigin="anonymous"></script>
      <script src="https://cdnjs.cloudflare.com/ajax/libs/popper.js/1.12.9/umd/popper.min.js" integrity="sha384-ApNbgh9B+Y1QKtv3Rn7W3mgPxhU9K/ScQsAP7hUibX39j7fakFPskvXusvfa0b4Q" crossorigin="anonymous"></script>
      <script src="https://maxcdn.bootstrapcdn.com/bootstrap/4.0.0/js/bootstrap.min.js" integrity="sha384-JZR6Spejh4U02d8jOt6vLEHfe/JQGiRRSQQxSfFWpi1MquVdAyjUar5+76PVCmYl" crossorigin="anonymous"></script>
      <script src="https://cdn.jsdelivr.net/npm/bootstrap@5.0.2/dist/js/bootstrap.bundle.min.js" integrity="sha384-MrcW6ZMFYlzcLA8Nl+NtUVF0sA7MsXsP1UyJoMp4YLEuNSfAP+JcXn/tWtIaxVXM" crossorigin="anonymous"></script>
      <div class="container">
         <h1>Bootstrap 4 information text about form</h1>
         <p class="text-info">This is Bootstrap 4 form</p>
         <h1>Bootstrap 4 form</h1>
         <form>
            <div class="form-group">
               <label for="name">Username</label>
               <input type="text">
            </div>
            <div class="form-group">
               <label for="pwd">Password</label>
               <input type="password">
            </div>
            <h1>Bootstrap 4 Button</h1>
            <button type="submit">Submit</button>
         </form>
         <p class="text-success">Thank You!</p>
      </div>
      <br>
      <br>
      <br>
      <div class="container mt-3">
         <h1>Bootstrap 5 information text about form</h1>
         <p class="text-info">This is Bootstrap 5 form</p>
         <h2>Bootstrap 5 form</h2>
         <form>
            <div class="mb-3 mt-3">
               <label for="name">Username</label>
               <input type="text">
            </div>
            <div class="mb-3">
               <label for="pwd">Password</label>
               <input type="password">
            </div>
            <h1>Bootstrap 5 Button</h1>
            <button type="submit">Submit</button>
         </form>
         <p class="text-success">Thank You!</p>
      </div>
   </body>
</html>

codemirror

Bootstrap 4 vs Bootstrap 5

Bootstrap is a free framework that is used to create responsive websites using a mobile-first strategy more quickly and easily. It is open-sourced framework. Colors in Bootstrap 4 are restricted. Custom form controls are included in Bootstrap 5. The form controls in Bootstrap 4 used whatever presets each browser offered. Because of its bespoke design, the form controls in Bootstrap 5 will have a much more uniform appearance and feel across all browsers. 

Bootstrap 4	Bootstrap 5
The Bootstrap 4 form has jquery.	The jquery is not utilized in Bootstrap 5.
Bootstrap 4 has less collection of colors.	Has vibrant and more colors available.
Browsers restrictions.	Bootstrap 5 improved the browser restriction.
It has 5 tier grid system.	It has 6 tier grid system.
The APIs cannot be customized.	Allows modifying APIs or develop own API.
The positioning feature is absent.	Columns can be positioned.
Less CSS usability.	More CSS properties also customized properties.
Uses default form development tools.	Better development of forms.
There is no offcanvas component.	The offcanvas component is added.
Bootstrap 4 provides normal form layout with no advance features.	Provides advance and attractive features to make forms.
Does not support RTL(right to left) switching in languages.	It supports RTL(right to left) switching in languages.
No themes customization.	Provides theme customization.
Small icon collection.	Large icon collection.