更新をクリックしたらフォーラムがダウンしました！

[Ed_S]

こちらで回答が見つかると思います：

Upgrade failed - could use some help to try and fix using SSH

Oh looks like you tried to enable Subfolder support with Docker but the first block indentation got messed up. All you need to is to add two extra spaces at the beginning of lines 82, 83, 84 and 85. After that save the file and rebuild.