What are the biggest challenges when building a fast social media tools website

I work in the social-media tools niche, particularly with tools related to TikTok, and I’m interested in how developers approach performance for websites with interactive tools.

What do you usually prioritize first: backend processing, JavaScript optimization, caching, database performance, or server resources?

I’d also be interested to know whether there are any common performance problems that developers tend to overlook when building browser-based tools.