Joplin Desktop/macOS: WebDAV/Nextcloud Sync not working over HTTPS

I am using Joplin 1.0.99 on macOS.

I have a WebDAV server that is reachable over HTTPS. The certificate has been signed by our own CA. The CA certificate is in the macOS keychain, accessing the WebDAV server using e.g Firefox is no problem.

When I try to set up synchronisation, I get the following error message when I try to check the config:

Error. Please check that URL, username, password, etc. are correct and that the sync target
request to failed, reason: self signed certificate in certificate chain (Code SELF_SIGNED_CERT_IN_CHAIN).

Apprently, Joplin does not consult CA certs in the keychain. Where do I have to store the CA Certs for Joplin to work?

Same problem here 2 years later.

Did you solve it? How?