In the Nginx configuration under "HTTP(S)" -> "Security headers," the web interface appears to be defective.
When creating a new security header or editing an existing one, the "Cancel" or "Save" buttons that are normally present are missing from all tabs.
(https://forum.opnsense.org/index.php?action=dlattach;attach=52567)
The tabs "Script," "Image," "Stylesheet," "Medium," "Frame," "Font," "WebSockets," "Worker," and "Form" cannot be accessed at all.
(https://forum.opnsense.org/index.php?action=dlattach;attach=52569)
Tested under OPNsense Business 25.10.2 (amd64) and OPNsense 26.1.2_5 (amd64) with both the Edge browser (145.0.3800.70, 64-bit) and Firefox ESR (140.7.1esr, 64-bit).
Addendum:
Under "Access," none of the buttons in any of the suboptions can be used anymore.
The same applies to "Miscellaneous" -> "SYSLOG destinations," as well as in the "HTTP(S)" tab, all submenus from "Cache path" downwards.