Configuring htaccess file for React Router on Apache Server

I have deployed a React app with React Router to my Bluehost server, and need to configure the htaccess file to redirect all of my routed URLs (/portfolio, /about, etc) to index.html instead of trying to fetch a new file from the server and throwing a 404.

I have read about countless similar problems in which the solution seems to be to add this into your htaccess file:

<IfModule mod_rewrite.c>
  RewriteEngine On
  RewriteBase /
  RewriteRule ^index\.html$ - [L]
  RewriteCond %{REQUEST_FILENAME} !-f
  RewriteCond %{REQUEST_FILENAME} !-d
  RewriteCond %{REQUEST_FILENAME} !-l
  RewriteRule . /index.html [L]
</IfModule>

I tried this, but I am still getting 404's when I try to visit any page of my site directly that isn't the homepage. I'm wondering if there is anything else in my existing htaccess file that is preventing the above code from working?

There was some code already in there from Bluehost, and I see another IfModule statement, so I'm wondering if that one is overwriting the first one. However I am afraid to edit it and break something, as it clearly says "do not edit." Here is my full htaccess code:

Header always set Content-Security-Policy: upgrade-insecure-requests

<IfModule mod_rewrite.c>
  RewriteEngine On
  RewriteBase /
  RewriteRule ^index\.html$ - [L]
  RewriteCond %{REQUEST_FILENAME} !-f
  RewriteCond %{REQUEST_FILENAME} !-d
  RewriteCond %{REQUEST_FILENAME} !-l
  RewriteRule . /index.html [L]
</IfModule>

# php -- BEGIN cPanel-generated handler, do not edit
# Set the “ea-php74” package as the default “PHP” programming language.
<IfModule mime_module>
  AddHandler application/x-httpd-ea-php74 .php .php7 .phtml
</IfModule>
# php -- END cPanel-generated handler, do not edit

# BEGIN WordPress
# The directives (lines) between "BEGIN WordPress" and "END WordPress" are
# dynamically generated, and should only be modified via WordPress filters.
# Any changes to the directives between these markers will be overwritten.

# END WordPress

Any ideas? I've double-checked that my BrowserRouter is set up correctly and also tried a few other htaccess configurations. I want to avoid using HashRouter or Node if possible but am getting frustrated. I can provide my React code as well if needed, but I'm pretty sure the error is not with the React setup.