Diagnose a slow cold load and a huge table in a web app

A web app is slow on its first load, and one page renders a table with a very large number of rows that makes the page sluggish. Explain how you would find the causes (profiling, network and bundle analysis, rendering cost) and fix them: shrinking and splitting the bundle, caching, deferring work, and for the table, pagination or virtualized rendering, memoization and avoiding needless re-renders.