Single/Multi Issue Picker
Issue Picker field allows you to select single or multiple issues from pre-defined issues. You can determine the list of issues using JQL and if you want, you can limit it to only the current project by selecting the "Limit selectable issues with the issues of the current project only" option.
As you can see, you can link the selected issues to the main issue. Additionally, you can also specify how you want the selected issues to appear on the field.
Please remember that you need to have Jira Administrator permissions for the user you are using to configure and create Single/Multi Issue Picker Fields.
Create Single/Multi Issue Picker Fields
Go to Issues → Custom fields
Click on the Create custom field button located in the top right corner.
Select All and Issue Picker Fields, and click Next.
Add a name and add a description if you want, and click Create.
Associate field your field to the appropriate screens, and click Update.
Configure Single/Multi Issue Picker Fields
Go to Issues → Custom fields
Find your field and click on the three dots located at the far right of your field's row.
Click Context and default value.
Click on the Edit custom field config option located at the bottom of the screen.