While modern operating systems come pre-packaged with newer versions (like .NET Framework 4.8 or .NET 8), these modern runtimes do not support legacy apps built for the 1.1 through 3.5 architecture. To run specialized legacy software, business tools, or older video games, you must explicitly enable or install this framework. Warning: The Danger of "dotnetfx 365.exe"
If you need the specific version that includes updates (some people call that "365"), you can extract it from a Windows ISO using DISM: dotnetfx 365.exe