Why has my series X reset itself after unplugging the power cable?

A bit of both, so whenever I load games now it’s just capped at 60 frames

Hi and thanks for reaching Microsoft Xbox gamer's community. My name is Josef.
I'm an Independent Advisor and a Microsoft Xbox user like you.

Hope you're doing great today despite this Alex

I found this odd.
So, just to confirm. The console went back to factory defaults after you disconnected the power cord accidentally?

Or do you mean that after connecting the console back to the power the 120Hz frequency can't be selected?

In any case and about this last problem, what monitor do you have? (Model)
Are you able to test the controller with a different 120Hz compatible screen?
Or what did you tried so far to fix this
In that way I can advise you different things or how to proceed

I have had the same issue , I took my xbox to travel , it worked fine when I was away but now it's reset it self when I plugged it back in at home

Please share the exact model, it needs to look like this "LG 27GL850 27'' "LG 27GL850 27"

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In the meantime, are you tried to use 4K + 120Hz?
If you try lowering the resolution the 120Hz option appears?

My current monitor is the LG Ultra gear 27 inch monitor