PluginRx

Simple Maintenance Redirect allows site administrators to enable maintenance mode by redirecting visitors to one of your specified pages (without header and footer) or an external URL instead of complicating things with all kinds of confusing settings. Logged-in administrators can still access the site normally, ensuring a seamless workflow while updates are made.
Features:
<ul>
<li>Custom Maintenance Page: Redirects visitors to a selected WordPress page while the site is in maintenance mode.</li>
<li>Maintenance Page Modifications: Automatically hides the header and footer on the maintenance page and adds a <code>maintenance-mode</code> class to the body element for further customization.</li>
<li>External Redirect Option: Redirect to an external URL instead of a WordPress page if needed.</li>
<li>Admin Bypass: Logged-in administrators can continue working on the site without redirection.</li>
<li>Developer Hook: Modify rules for when a user should be redirected.</li>
</ul>
How It Works:
<ul>
<li>Create and publish a page with your custom maintenance message.</li>
<li>Go to Settings > General and choose a Maintenance Mode Page or enter an External URL.</li>
<li>When enabled, visitors will be redirected to the selected page or URL. Logged-in administrators can still access the site.</li>
<li>The plugin does not affect the login page, REST API, or JSON endpoints.</li>
</ul>
This plugin is great for “coming soon” pages, staging site protection, design previews, or any situation where you need to hide the main site while keeping access for yourself.
<h3>Demo</h3>
<iframe loading="lazy" class="youtube-player" width="750" height="422" src="https://www.youtube.com/embed/DTKGftmpBQ4?version=3&rel=1&showsearch=0&showinfo=1&iv_load_policy=1&fs=1&hl=en-US&autohide=2&wmode=transparent" allowfullscreen="true" style="border:0;" sandbox="allow-scripts allow-same-origin allow-popups allow-presentation allow-popups-to-escape-sandbox"></iframe>

Simple Maintenance Redirect

Easily redirect visitors to a maintenance mode page or external URL while keeping access for logged-in administrators.

elsteno

Creates a Soon Online Page (cooning soon) that is visible by all not logged in wordpress users. 
It is very useful for new sites that are underconstruction!

WPsoonOnlinePage

Creates a Soon Online Page (cooning soon) that is visible by all not logged in wordpress users.

Simple Maintenance Redirect vs WPsoonOnlinePage