This may help:
https://support.microsoft.com/en-us/win ... baebeebc85Basically, what I'm reading here is that you have your device configured so that you can only run apps downloaded directly from the Microsoft Store. I've not tested it, but you probably aren't going to be able to install Java*, either, which is required to run Haven.
If you want to turn 'S mode' off so that you can install your own applications, instructions are in the FAQ I linked. Warning: it's a one-way change.
*Dug around a bit more. no, you cannot install Java while in "S mode." While several Java based items are available on the MS Store, they're programmer and student tools and references.
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