I am currently trying to reach my own web-service via Chromium on Android 8.1 I have installed the Certificate for the Server, but when I try to reach my service I get a "Your connection is not private" Error.
To install the CA I have downloaded it via Chrome on my desktop and pushed it via USB to my phone.
I then went to Settings -> Security & Location -> Encryption & credentials -> Install from storage and installed it.
The Phone is in the same network as the server is and it knows the FQDN and IP of the server
Edit 1: To clarify further: it's a self-signed Cert, so the certification-path contains only one certificate, that of the server