Keyboard and mouse only works with Gold account user and no others

Have you tried this?

To assign an account to a controller, follow these steps:

1. Press the Xbox button  to open the guide.
2. Select System > Settings > Devices & streaming > Accessories.
3. Select the controller, and then the More options icon (…). Assigned to shows the current account assigned to that controller.
4. To assign the controller to another account, select Assigned to, and then select the account that you want assigned to the controller. This will pair the controller to this account.

[quote user="Luckydan77"]

If you get a wireless mouse and keyboard from Microsoft it will be compatible and should work just fine.

[/quote]

that will not work - you can only use a keyboard for messages, the mouse will not work

as others have said a 3rd party adaptor is needed

For the following to work you must make the menu selections using your keyboard. If you use the controller to make your menu selections to start the game you will be placed in a room for those with a controller and your keyboard/mouse will be non functional
to make it fair to other players. To enter the room for keyboard and mouse users the game must be started by selecting the options using the keyboard/mouse. Hope this helps.

Mouse and keyboard support

Fortnite on Xbox One supports the ability to play with a mouse and keyboard. Note that when using a mouse and keyboard on Xbox One, you’ll be placed in a game with other users who also chose mouse and keyboard as their control option. To enable your setup
to use mouse and keyboard, see Mouse and Keyboard Support

Note If you’re on a child account, you’ll also need to enable settings for cross-network play to use a keyboard and mouse while playing
on Xbox One.

Hello, bertrand. Thanks for reaching out! My name is Lucas, and I'm an Independent Advisor and a Microsoft user just like you. I'll be happy to assist you today.

Try to change the keyboard language in your xbox settings. Some users went from QWERTY French-Canadien to QWERTY English and it worked. Or English UK to English US.

Also, the keyboard and mouse will usually only work for the first account signed in to the console. If you have more than one, please try to sign off the other accounts and then try to plugin the mouse and keyboard again.

Just to make sure, did you select the in-game option to use mouse and keyboard and assigned them to your account? And are you using both of them connected to the console?

Waiting for your kind reply.

Hi,

A keyboard and mouse, wireless or wired only work on a very limited selection of games (about 30+) for other games it's controller only. All Xbox One games with mouse and keyboard support

Keyboard and Mouse on Xbox One and Series X|S