A is incorrect: While `Concurrent()` can execute multiple actions simultaneously, it still runs within `App.OnStart`, meaning the app remains blocked until all concurrent operations complete. This might offer a marginal improvement but does not address the fundamental issue of synchronous blocking initialization.

B is incorrect: Moving variables to `OnVisible` of the first screen would simply shift the loading delay to when that specific screen becomes visible, potentially causing a visual flicker or a delayed experience for the user on that screen.

C is correct: Named Formulas, declared within the `App.Formulas` property, represent the contemporary and recommended method for establishing global states, design themes, and application configurations. They benefit from 'lazy evaluation,' meaning the Power Apps engine computes their values solely when a specific screen or control explicitly references them, thereby eliminating the `OnStart` bottleneck and significantly improving initial launch performance.

D is incorrect: `UpdateContext()` is used for screen-specific context variables and does not offer a global solution for application-wide state or configuration in `App.OnStart` that would alleviate startup delays more effectively than `Set()` functions.