1698, "Access denied for user '_58bbb20468ca032a'@'localhost'

WARNING: this is potentially destructive - deletes the current DB and creates a new one, so adapt to your needs BEFORE you try it
In one of my install scripts I found this note…

cd $HOME/frappe-bench;
bench new-site $erpnextSiteName;
    # You'll be then prompted to input your MySQL root password.
      # IF this happens....
      #ERROR 1045 (28000): Access denied for user '_8de49ae55a02e7ac'@'localhost' (using password: YES)
      DBname=$(cat ~/frappe-bench/sites/$erpnextSiteName/site_config.json | awk '/db_name/ {print $2}' | sed "s/\"//g" | sed "s/,//g");
      # delete the DB & site, and then retry
      mysql -uroot -p$MySQLpwd -Bse "drop database $DBname;"
      rm -fR $HOME/frappe-bench/sites/$erpnextSiteName;
      bench new-site $erpnextSiteName;
    # You'll also be prompted to create a new password for the System Administrator.

Check if your mariadb service is running and try creating a new site again.

sudo service mariadb start

If that still doesn’t fix it, then you might want to check on the mariadb installation.