itthinx

This plugin redirects 404’s caused by hits on pages that are protected by <a href="https://wordpress.org/plugins/groups/" rel="ugc">Groups</a>.
The redirection settings can be adjusted in Settings > Groups 404 :
Visits to protected pages can be redirected to:
<ul>
<li>a specific post, or</li>
<li>the WordPress login</li>
</ul>
The redirection can also be applied for restricted categories, tags and other taxonomy terms if <a href="https://www.itthinx.com/shop/groups-restrict-categories/" rel="nofollow ugc">Groups Restrict Categories</a> is used.
The redirect status code can be selected among:
<ul>
<li>Moved Permanently (301)</li>
<li>Found (302)</li>
<li>See other (303)</li>
<li>Temporary Redirect (307)</li>
</ul>

Groups 404 Redirect

I know this plugin hasn't been updated in a couple years, but IMHO Groups and its related plugins (like this one) are a hidden gem for WordPress sites. So many people jump to complicated membership plugins when they could do everything they need with Groups. This 404 redirect add-on works like a charm. I'm using it on the latest version of WP 5.x

Perfect.

Redirect 404's when a visitor tries to access a page protected by Groups.

wptobe

The easiest, fastest and most reliable membership plugin
The wptobe-signinup plugin provides functions for member registration, login and member management required on the website, 
It focus on ease of use and fast speed and stability. It offers a Captcha function to protect against spam by default and easily change the design of any theme by selecting a pre-made template without any programming.
Member Registration, Login, Reset Password, Profile, Change Password. 
우커머스 쇼핑몰 체크아웃 국내 주소(Daum 우편번호 서비스) 사용 기능.
<ul>
<li>
The capcha can be used for sign-in/sign-up screen to prevent spam users.
</li>
<li>
Each field can be edited and the position can be easily changed by drag-and-drop. The setting screen and the short code output are the same, so it is very intuitive and easy.
</li>
<li>
It provides on/off switch to show or hide each field.
</li>
<li>
It is possible to log in by email without username.
</li>
<li>
You can set the page to be redirected after sign-in/sign-up.
</li>
<li>
No need to put the short code directly in a page, just select it from the selection box.
</li>
<li>
You can create different styles and change them whenever you want. For example, create a themeA, themeB C style whenever the theme changes, simply change it in the selection box to change the design. We provides Default/Black/Avada/Enfold design by default.
</li>
<li>
It allows users to receive via email if they forget their password. The administrator can modify the content of the email to be sent.
</li>
<li>
Members can change their current password to a new password on the profile page.
</li>
<li>
It provides an html/css file that outputs sign-in/sign-up/profile independently, so you can easily change and copy it.
</li>
<li>
You can reset the plug-in to the initial state at any time.
</li>
</ul>
<h4>User Guide</h4>
You can find user guide, installation and more detailed information about Wptobe-signinup on wptobe.com. 
* <a href="http://www.wptobe.com/wptobe-signinup" rel="nofollow ugc">User Guide</a>

Wptobe-signinup

Wptobe Signinup is a very light plugin that lets you easily and safely build sign in/up with designed page.

Groups 404 Redirect vs Wptobe-signinup