Backend Stack suggestion for multi-platform app

#php #javascript #node #beginners

Hello,

I am working on a side project, and having difficulty of choosing the right stack to work with.
The problem Im facing is how to manage users in the platform.
I want to use PHP for web , because of SEO mainly. My site will include thousands of products , and after reading quite a bunch, a JS app can never have the same SEO as php\asp, mainly because of search engines algorithms.

So Im using php for web, and react-native for mobile.
The question now, is what to use for backend. Can I integrate users sign-in and sessions with JS on a php website?

Or my only point of connection between the website and the mobile apps will be the Database and thats it?

I am a new beginner and looking to understand the right way to integrate different platforms. Also if you have some support or suggestion for easing development and platform management I would highly appreciate it.

Thank you