PageSpeed speed index slow on practically empty React app
I am using Django on the backend and running React on the frontend inside Django app. I have created very basic frontend with loading animation until React loads in and few components with navigation and heading. That's basically it. I wanted to have a very basic starting point and test it for page speed so I deployed the project to railway and tested it out. But even after fixing all the problems that PageSpeed Insight suggested I can't get the mobile version above 88. 
Under the network tab I can see that main.js is by far the biggest content download but at the same time 324kB doesn't seem like too much.
I don't know what else to improve anymore as it's such a basic app. What is causing the main.js to be downloaded so slowly?