How can I process millions of data quickly on the web?

I'm trying to show you six million data on the web chart, but it's too slow. I use golang, mongodb, React, plotly.js as chart library 6million data takes very long time. It takes 10 seconds to retrieve the data from the server. It takes 1 second to make it json. How can I improve the performance? I said we should reduce the amount of data, but my employer says we can't.