Since the game is now considered (software no longer supported or sold by its creator), community-driven sites are your best bet:
Some users report needing specific older DirectX files or Visual C++ Redistributables to launch the game successfully. Gameplay Tips & Walkthroughs dexter-the-game-pc-game-free-download-full-version
If you find a download, follow these general steps to get it running on modern Windows: Since the game is now considered (software no
Users often share the PC port here. It is generally the go-to for titles that can't be bought legally. dexter-the-game-pc-game-free-download-full-version