KopiaUI: WebDav with self-signed cert?

I want to use KopiaUI (0.15.0) with WebDAV on my local network.
The WebDAV server has a self-signed cert.

When accessing the SSL WebDAV path with KopiaUI, I get an error message: No valid authority.
I don’t see seeting in KopiaUI to allow this self signed cert.

How to do that?

This is not really kopia problem. Kopia uses OS to validate it.

Register your self signed authority as trusted in your OS.

Google will tell you how, e.g.: