None of the gamebar or Xbox which I never downloaded from the Windows store will...

xbox is part of microsoft windows and has been for a long time, the apps and services dont take any space. as microsoft moves to being more of a service than just a plain software company you will see more and more changes overtime, dont forget windows 10
is a service not a static operating system anymore, hence why they gave it away for free initially.

you can remove it with command line instructions but when you get the next major update it will be back again.

when you signed into windows for the first time you agreed to the terms and conditions, Microsoft can add or remove any apps or service as and when they want. If you dont want this then you would have to use windows as an offline OS and disconnect from
the internet.

that will not work, the gamebar is ONLY updated via the windows store not windows update. he has the non updated version, no need to go and reset this and that, its simply a case of opening the windows store and selecting get updates, this will then download and update the gamebar to the latest version.

uninstall gamebar and then re install from the windows store

check for updates under windows store, if not uninstall gamebar and install from the store.

check windows store for gamebar update, if not then uninstall gamebar and re install.