This is the documentation for Clone Plus for Jira Cloud. If you using Clone Plus for Jira Sever/Data Center, refer the Bulk Clone - Server page.

This page provides details of the Bulk Clone feature where you can clone multiple issues from multiple projects at once. You can select these issues to be cloned using Jira JQL basic or advanced search. You can also perform bulk cloning on saved Jira filters.

The bulk clone operation is applied to a maximum of 1000 issues in a project. If a project has more than 1000 issues, the remaining issues are ignored and are not cloned.
The Bulk Clone (Clone Plus for Jira) button is available only when you access issues from the Filters dropdown in the top navigation bar. This button is unavailable when you access issues from the Projects dropdown in the top navigation bar.
Do not close your browser or let your computer go into sleep mode once the bulk clone operation starts. This is to ensure that the bulk clone does not terminate prematurely. You can still work on other tabs of your browser to allow the bulk clone operation continue in the background.

You also refer the following various clone features using bulk clone:

Page:

Bulk Clone Jira Filter Issues
Page:

Clone all Issues in a Project - Cloud

Steps

In the top navigation bar, click Filters > Advanced issue search to search for the issues you want to clone using advanced search or click Switch to basic next to the search bar for a basic search.
Or
In the top navigation bar, click Filters > <filter name> to navigate to one of the saved filters.
In the top-right corner, click Bulk Clone (Clone Plus for Jira).
On the Choose issues page, select the issues you want to clone. You can also select all the issues by selecting the checkbox from the first column in the heading.
Click Next.
On the Bulk Clone details page, do the following:
1. In the Clone operation field, select the clone operation which you want to apply to the issues being cloned.
2. In the Project field, select the project to which you to clone the issues.
3. In the Issue type field, select the issue type you want assign for the issues being cloned.
4. In the Clone options section, click the required clone option.
Click Next.
In the Confirmation page, review the Issues selected and Bulk Clone details sections.
Click Run Clone to clone the selected issues.
The selected issues are cloned as configured. You can see the Clone report with the following details:
Click View clone(s) to view all the cloned issue(s).

You cannot clone a subtask to the same (subtask) issue type. If you clone a subtask to the same (subtask) issue type, you will see a warning message.
When you select the Attachments option, the images or any form of media added to rich text editor fields such as description, comments, or environment, are copied to the cloned issue during bulk clone. If this clone option is not selected, a broken image is displayed in the respective field of the cloned issue.
In the Issues selected section, the issue list is paginated and a maximum of five issues are displayed per page. Click or to navigate to the next and previous pages respectively.
You can go to any page at any point during setting up the details for bulk cloning, and the details provided in each page are retained.