Improve a React.js/Gatsby.js website

I would like some help from an experienced React.js developer in improving the performance of my React.js/Gatsby.js website. I want to decrease its load-time latency. I also want to improve its UX (user experience). Additionally, I want to make the site responsive on multiple devices, particularly devices using the Facebook browser (mobile phones), but also on desktop browsers, Samsung Folding Smartphone, etc.