The PCGamingWiki recommends "ThirteenAG's Widescreen Fix" for modern resolutions, which is typically downloaded as a .zip file and extracted into the game directory. Downloads - Rockstar Games

If you already own the original PC version and need to update it or fix widescreen issues:

Rockstar provides a v1.1 patch to resolve stability issues.

The Definitive Edition is available on Steam and requires a modern 64-bit processor and 8 GB of RAM. Technical Support and Patches

To download Grand Theft Auto III (GTA III) for mobile (Android), you can access the official game through the Google Play Store . For the "Definitive Edition," a version is also available via the Netflix mobile app for subscribers. Official Purchase and Download Options

Available as a direct purchase for iPhone and iPad.

You can purchase and download the Grand Theft Auto: The Trilogy – The Definitive Edition directly from Rockstar Games .