if you buy a digital xbox game on the website can you download it onto your xbox?

Yes. Just make sure you're signed into the same account you use on the console.

2 options mate, you can buy the disc. Which will download a digital version onto your Xbox, although you will still need the disc in to play. Or you can buy the games from Xbox.com

@Alice, Yes you can:

www.xbox.com/.../games-with-gold

Just "buy" them through the website and when you get your Xbox go onto "my games & apps" and they'll be there ready to download.

Or just buy the game xmas eve so it's there for you on xmas morning.

Or buy the game for you xmas morning & by the time you've spent the day with your family it will be downloaded ready for you to play.

Leaving it to the last minute to buy a digital download isn't really an issue is it?

No need for your idea really but you can still post it on the feedback site
here

Did you download your Microsoft account, onto another Xbox device? If so, digital purchases are part of that account. Search your version of Modern Warfare, and check the Microsoft Store for your purchased version.

You might be using Game Pass, or a free to play variant. If your brother's account owns that Modern Warfare game, your account can not download the game.

The owner of the digital copy of the game, has the rights for downloading onto a new Console or PC.