VCL dual‑project versus FireMonkey single‑source for Windows/macOS RAD Studio applications

When targeting both Windows and macOS with RAD Studio, a developer can either maintain two separate VCL projects—one compiled for each OS—or adopt a single FireMonkey codebase that builds for both platforms. The goal is to choose the approach that satisfies the need for native Windows look‑and‑feel and direct Win32 API access while keeping overall maintenance effort low and runtime performance acceptable on both operating systems. Uncertainty remains about how the performance gap and UI fidelity differences translate into real‑world development effort and user experience.

Which option provides the best trade‑off between startup performance on Windows and visual fidelity on macOS? How does the maintenance overhead of dual VCL projects compare to the single FireMonkey codebase over a typical release cycle? To what extent does limited direct access to Windows‑specific APIs in FireMonkey affect the ability to implement platform‑dependent features?