I checked [the GitHub mirror](https://github.com/vor0nwe/npp_preview) as well and did not find a license file. The only mention of any kind of license is in [the borrowed source files](https://github.com/vor0nwe/npp_preview/tree/master/src/lib) from Damjan Cvetko's [dbgpPlugin](https://github.com/zobo/dbgpPlugin).

Given how copyleft licensing works, I would assume the entire project is under the dbgpPlugin license as it's ["based on"](https://github.com/vor0nwe/npp_preview/blob/1113731214f304aa87897c560233d067c47213f7/src/F_About.dfm#L50) the dbgpPlugin code; in other words:

> Linking a GPL covered work statically or dynamically with other modules is making a combined work based on the GPL covered work. Thus, the terms and conditions of the GNU General Public License cover the whole combination.
>
> <https://www.gnu.org/licenses/gpl-faq#GPLStaticVsDynamic>

But that may not be what you intended; e.g., maybe the original code is under a different license, one that's ["compatible" with the GPL](https://www.gnu.org/licenses/license-list.html#GPLCompatibleLicenses)?

It would be great if you could be more specific. Forking a project with no explicit license is O.K. as far as GitHub's [terms of service](https://docs.github.com/en/site-policy/github-terms/github-terms-of-service#5-license-grant-to-other-users) are considered. But changing the code or publishing a new version under a different author is technically illegal in jurisdictions that recognize the Berne Convention, unless there's a public license granting those permissions.