Search for OBS from the Start Menu, right-click on it, and hit Open file location. Right-click on OBS Studio in Explorer and select Send to... Desktop (create shortcut). Right-click on the OBS Studio shortcut on your desktop and select Properties. In the Target box, add " --startstreaming" after the last quote. Press Windows logo key + R, type shell:startup, then select OK. Copy the desktop shortcut into the startup folder.
YouTube is funny about broadcasts. You will need to get everything set up in advance, linking accounts, and broadcast setup.
Let me know if this works for you!