With the release of the September 2025 Cumulative Update for SharePoint, Microsoft has made changes to permissions that may cause solution deployment to fail, which ultimately will cause the Nintex for SharePoint installer to fail. The issue has been acknowledged here and, according to this page, a fix is planned in the coming October 2025 CU.

I’d suggest avoiding this scenario if possible. However, if you must run the Nintex for SharePoint installer while your environment is on the September 2025 CU, please review the links above for workarounds.