Microsoft Teams currently requires at least Windows 10 to run the "New Teams" client and most modern versions of the "Classic Teams" client. There is no official "Windows 8.1 version" available for download on the Microsoft website today.
After installation, you may see a yellow banner: "Your Windows version is out of support. Some features may not work."
The primary reason behind this incompatibility lies in the underlying architecture of Windows. Windows 8.1 relies on an older code base that Microsoft has moved away from.
Windows 8.1 is . For Teams to work properly, upgrade to Windows 10 or 11 (64-bit). If that's not possible, use the web version as your only reliable option.
It is worth noting the distinction between the two versions of Teams: