Operating system compatibility

None of the versions that are currently officially available are compatible at all with Windows 8.1. The last version of Premiere Pro that was compatible with Windows 8.1 was version CC 2018 (12.x), which officially became no longer available in late 2019 with the release of version 2020 (14.0). Adobe now officially restricts version availability to the two latest major versions as per the company's new older version availability policy which went into effect in May 2019.

Beginning with CC 2019 (version 13.0), Windows 10 is now required. Windows 10 will become officially discontinued this Fall with the release of Windows 11, which requires a CPU that's no more than four years old (at the time of Windows 11's official release) in order to even run at all. Windows 10 will  continue to be supported on older PCs with at least one new feature update and numerous security fixes until October 14, 2025.

No

https://helpx.adobe.com/creative-cloud/system-requirements.html
-Win7 is dead https://www.microsoft.com/en-us/windows/windows-7-end-of-life-support-information
-Win8 is also no longer supported https://support.microsoft.com/en-us/help/4580358/windows-8-1-update