Issue Summary

This is reproducible on Data Center: yes

This seems a consequence of "The Rich Text gadget substitutes the deprecated Text gadget":
https://confluence.atlassian.com/jirasoftware/jira-software-9-11-x-release-notes-1272283668.html#JiraSoftware9.11.xreleasenotes-rich-text-gadget

Steps to Reproduce

1. Enable the module Text Gadget (deprecated)
2. Add a gadget to a dashboard with a link to the same Jira instance with target="_blank" attribute

Expected Results

The link would be opened in a new tab like it was in Jira 9.4.

Actual Results

The gadget definition is saved without the target attribute and the link opens in inside the gadget.

The replacement Rich Text Gadget also has a hard coded behavior that external links are opened in new tabs (as defined in the User Profile), but "internal links" are only opened inside the gadget.

Workaround

Admins may add this Feature Flag (no need for restart):

com.atlassian.jira.security.text.gadget.output.sanitization.disabled

(ref.: How to manage dark features in Jira)

Though note the sanitization of the Text Gadget was meant to prevent security vulnerabilities.