Install Synology DSM 7.2 on a PC (Updated)

DSM provides flexible options for handling SSL certificates. Users can generate a self-signed certificate, which is quick and useful for internal networks, or install a certificate from a trusted Certificate Authority (CA) for public access. Trusted CA-signed certificates eliminate browser warnings and ensure users that the NAS is legitimate. Certificate management in DSM is centralized in the Control Panel under the “Security” and “Certificate” sections. Here, administrators can create, import, and assign certificates to various services, including the DSM Web GUI.

https://vital-mag-net.blog/dsm-7-1-setup-configuring-the-web-gui-to-https/