Add Custom Table can't see the table

me too.
It can only display the tables in the Drupal system. I hope someone can improve it too.

You might want to try version 2.0.6

also, it's good to read the README.md

https://git.drupalcode.org/project/view_custom_table/-/blob/2.0.x/README.md

VIEWS CUSTOM TABLE

CONTENTS OF THIS FILE

1. Introduction
2. Requirements
3. Installation
4. Configuration

INTRODUCTION

The Views Custom Table module gives the functionality to integrate your custom
table to views. So you can use strong features of the views for your custom
table. This module use hook_view_data() to implement functionality.

For a full description of the module, visit the project page:
https://www.drupal.org/project/view_custom_table →

To submit bug reports and feature suggestions, or to track changes:
https://www.drupal.org/project/issues/view_custom_table →

REQUIREMENTS

This module requires the following modules:

Views (Drupal Core)
Views UI (Drupal Core)

INSTALLATION

Install as you would normally install a contributed Drupal module. Visit:
https://www.drupal.org/docs/extending-drupal/installing-modules →
for further information.

CONFIGURATION

Configure user permissions in Administration » People » Permissions:

Add custom table in views

• Give user access to add his custom table to the system.

Administer all custom table in views

• Give user access to administer all the custom tables, added by all the users

Administer own custom table in views

• Give user access to administer own custom tables

Manage custom tables in Administration » Structure » Views » View CustomTable menu.

Alternately, there's instructions on the project page: →

How to use:

1. Download and extract files in module folder.
2. Enable module from module list
3. Go to Home » Administration » Structure » Views » View Custom Table
4. Add your custom table in system using "Add Custom Table" link
5. Add Relationship with drupal entities if any, otherwise leave none.
6. Clear drupal cache
7. Add a new view and you will see your custom table name in "Show" drop-down field.