Since you cannot download the official Game Bar, you can use these top-rated third-party tools to get the same (or better) recording and performance tracking features:
: Part of GeForce Experience, this tool uses your graphics card to record with almost zero performance hit. xbox game bar download windows 8
Xbox Game Bar Download for Windows 8: Everything You Need to Know Since you cannot download the official Game Bar,
: The original "Xbox Games" app for Windows 8.1 was discontinued in 2018. xbox game bar download windows 8