If you can access your WordPress site but got 404 not found error on blog post or category page or tag page etc. It typically because your .htaccess file content is not be in-place and so your URL cannot rewrite to the chosen permalink. Here below is the default .htaccess content of every WordPress Blog

# BEGIN WordPress

RewriteEngine On
RewriteRule .* - [E=HTTP_AUTHORIZATION:%{HTTP:Authorization}]
RewriteBase /
RewriteRule ^index\.php$ - [L]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /index.php [L]

# END WordPress

To fix this issue, just login to your WordPress blog and go to Settings > Permalinks and click on “Save Changes” button

After click “Save Changes”, .htaccess file will be generated automatically and you can test by open your blog post URL again.