How can I optimize NextJS first load pages?

I am using Nextjs 13.5 with Pages structure in building a large scale application that consists of many complix logic and components.

I alwayse make sure to separate my logic and sections in one page into small components.

However, I am facing an issue with First Load JS time as many of the application pages taske long time to load and render.

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I have tried improving my code a lot, removing unnecessary codes, using dynamic content, writing clean code but still the problem is there.

I just want to know what are the factors that increase the loading of such pages? And what can I do to reduce it.