yii2无法使用htaccess访问root子文件夹

I'm really bad at htaccess setting and would like to have some help with it. I have a project inside a subfolder, and can be opened like this: www.mydomain.com/subfolder/. I put my project inside "subfolder". "subfolder" is not a subdomain, I just simply created a new folder in root folder.

I can open home page, but all other page like www.mydomain.com/subfolder/about, www.mydomain.com/subfolder/product have 500 internal server error page. I also can't access uploaded file in uploads folder, so URL like www.domain.com/subfolder/uploads/filename.jpg will return error 404. I'm pretty sure that there is no php error becase I also uploaded it in my other subdomain (different domain) and it works fine.

This is my htaccess setting:

Options +FollowSymlinks
RewriteEngine On

RewriteCond %{REQUEST_URI} /(backend)
RewriteRule ^backend/assets/(.*)$ backend/web/assets/$1 [L]
RewriteRule ^backend/css/(.*)$ backend/web/css/$1 [L]
RewriteRule ^backend/font/(.*)$ backend/web/font/$1 [L]
RewriteRule ^backend/plugins/(.*)$ backend/web/plugins/$1 [L]
RewriteRule ^backend/images/(.*)$ backend/web/images/$1 [L]
RewriteRule ^backend/js/(.*)$ backend/web/js/$1 [L]

RewriteCond %{REQUEST_URI} !/backend/web/(assets|css|font|plugins|images|js)/
RewriteCond %{REQUEST_URI} /(backend)
RewriteRule ^.*$ backend/web/index.php [L]

RewriteCond %{REQUEST_URI} /(assets|css|js|img|fonts|uploads)
RewriteRule ^assets/(.*)$ frontend/web/assets/$1 [L]
RewriteRule ^css/(.*)$ frontend/web/css/$1 [L]
RewriteRule ^js/(.*)$ frontend/web/js/$1 [L]
RewriteRule ^img/(.*)$ frontend/web/img/$1 [L]
RewriteRule ^fonts/(.*)$ frontend/web/fonts/$1 [L]
RewriteRule ^uploads/(.*)$ uploads/$1 [L]

RewriteCond %{REQUEST_URI} !/(frontend|backend)/web/(assets|css|js|img|images|fonts|uploads|plugins|font)/
RewriteCond %{REQUEST_URI} !index.php
RewriteCond %{REQUEST_FILENAME} !-f [OR]
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule ^.*$ frontend/web/index.php

Could someone help me?