HTTPS communication ensures information such as the user name and password is encrypted when passed from the browser to the camera/NVR. This is facilitated by the use of SSL Certificates.
Certificates can be bought from a Certificate Authority, but its also possible to create self signed cert using SSL. A self signed cert is one that is issued by a general user and not a CA.
OpenSSL can be used to create a Self Signed Certificate and Private key, with the following command:
openssl req -x509 -sha256 -days 1000 -newkey rsa:2048 -keyout rootCA.key -out rootCA.crt
The Certificate .crt file and Private Key .key file, that are created with the above command are installed on the camera here:
While the connection is still encrypted, the browser does not recognise the certificate. This is because it was not issued by a Certificate Authority (CA). The browser will warn you the cert is not valid and the web page is not secure. A malicious third-party could be redirecting the connection using another self-signed certificate bearing the same holder name meaning the website might be not be the intended target i.e. a fake web site made to look like the intended one
This is just a warning from the browser and does not mean there is an issue with the camera or NVR web site.