If you are looking for an offline installer for compatibility, you can find the Microsoft .NET Framework 4.8.1 offline installer on the official Microsoft Support site.
: You should only download official installers directly from the Microsoft .NET Download page to avoid potential malware bundled with fake "version 4.9" installers. .NET Framework 4.9 Offline Installer for Windows
Using the links above, download NDP481-x86-x64-AllOS-ENU.exe . The file size is approximately . If you are looking for an offline installer