This may be more of an Android issue than self-hosting, but i run Radicale on my personal server to host caldav/carddav services. I want to login with uname&pword with a certificate. I found this video in Davx5 github page showing that a user can select the cert:
I generated a self-signed cert from my server and installed that to my Android phone via Settings > Security&Privacy > Encryption&Credentials. But i dont get the same as the video. It keeps telling me No certificate found
Clicking the install button and selecting my cert will say
Install CA certificates in Settings This certificate from null must be installed in Settings. Only install CA certificates from organizations you trust.
Add a certificate to the endpoint using your reverse proxy