Xbox One Developer Mode Not Activating -

Hi there, Nils28!

We would not recommend enabling developer mode on the console, unless you are a developer who is in the process of creating a new application.

Additionally, the developer mode for the Xbox One console would not allow others to install a virus on accounts. We'd recommend reading over the

Developer Mode Activation App FAQ for further clarification in regards to this.

Hello Václav Reitmaier,

Thank you for posting in the Microsoft Community.

It's really important for us to work on this so you can get back to what you're doing. However, it would be more beneficial if we posted this question on the Microsoft Q&A Forum. and since you have communicated with us first, we will make sure that your time is worth guiding you in the right direction where you can achieve the desired resolution. We would like to provide you with this link where you can send your concern to our Ask a question - Microsoft Q&A. We are confident that you will get the most relevant information and the best resolution for your concern.

Please see this page that has various FAQ on the developer mode:
https://support.xbox.com/xbox-one/apps/developer-mode-activation-app-faq

Also see here how to turn off developer mode:
https://docs.microsoft.com/en-us/windows/uwp/xbox-apps/devkit-deactivation

This includes formatting the console to factory settings - this would fix your problem.

Hello!

Thanks for reaching out to us here on the forums with this situation. I understand you're having issues with setting up a console into developer mode is that correct? Take a look at this helpful support article:

Developer Mode Activation App FAQ

Hope this helps!

Hello, from what I researched you can only have a limit of 3 devices. I haven't found anything yet that talks about increasing devices.

Xbox One Developer Mode Activation Program | Microsoft Docs