What happens during Swift app startup and how can you optimize launch time?

App startup involves dynamic linking, static initialization, and main thread setup; optimization reduces work in early phases.

During startup, dyld loads frameworks, initializes global/static variables, runs UIApplicationMain, and constructs initial UI. Slow startup is caused by heavy static initialization, excessive framework loading, and synchronous work on the main thread. Optimization includes lazy loading, reducing dynamic frameworks, and deferring non-critical initialization.