Not the right topic, but if you get that error:
ln: failed to create symbolic link '/usr/share/yunohost/admin/ca.crt': File exists
I used to get it at every update for the yunohost-admin package, and working on another issue helped me figure out where it was coming from.
See [Solved] Cannot create subdomain anymore - #3 by matlag
I had deleted a certificate file I probably thought irrelevant at the time. Putting it back fixed it for me.