hi @Amari welcome to the forum 
for Docker setup please always post you docker run commands or docker compose file.
your posted logs complains about
"user": "admin",
"message": "Failed addUser attempt with hint exception.",
"version": "29.0.5.1",
"exception": {
"Exception": "OC\\HintException",
"Message": "Password needs to contain at least one lower and one upper case character.",
I’m wondering if it is the same with the browser. Please report how the browser login works (from the same machine where desktop client fails) post F12 logs if it fails. if your PW doesn’t meet the requirements please change and retry with the desktop client.
The other message
"message": "fopen(/var/www/html/config/config.php): Failed to open stream: No such file or directory at /var/www/html/lib/private/Config.php#221",
might be related to
if this is a new installation.