No, you cannot use a self-signed certificate for a domain:
- Headwind MDM and other applications will throw an "Untrusted certificate" error while attempting to access the website;
- It is not possible to add a self-signed domain certificate as trusted by Headwind MDM, it still couldn't be trusted by the OS.
See how to set up HTTPS on the LAN here:
https://h-mdm.com/private-network/
The easiest and recommended way is to install Headwind MDM on an "Internet" domain (you'll need to set up an appropriate DNS record in your LAN).
A far more complicated alternative is to set up a local CA chain (root and intermediate certificates) in your LAN, and use them to sign the certificates of your local domains.