Try
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Open Xbox app and sign out.
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Then, open Microsoft Store app and sign out.
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Go to Windows Settings → Apps → Installed Apps, click the three dots next to Gaming Services, and select Uninstall.
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Restart PC.
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Open Microsoft Store app and sign in.
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Then open Xbox app and observe the progress from 0% to 100% - this is when Gaming Services is being installed.
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Finally, sign in to Xbox app and launch MSFS.
Did you make sure that you are not joined to the PC Gaming preview?