As noted, LOCALAPPDATA\stellarium is left behind on your system when run.
I have tested on a clean Win7 system.
Fortunately, there's a simple fix that can be implemented for the next revision. See here.
New: OneLoupe (May 1, 2025), Platform 30.0.2 (Mar 27, 2025)
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This is fixed in Stellarium Portable 0.13.0.
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