TLDR:
I confirm after changing Microsoft Store Account and then reinstall Microsoft Flight Simulator (MFS) via Store without downloading full packages WORKS.
What I did:
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Move contents of Packages\Official\OneStore folder (and Community if you want) to another drive. This for backup. In case this BIG files/folders deleted too when uninstall MFS 2020;
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Uninstall MFS 2020. Right click its icon from Start Menu → Uninstall;
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Open Microsoft Store. Click your old profile account → Sign Out;
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Right click Microsoft Store from Start Menu → App Settings, after Settings app page shown, click Reset Microsoft Store;
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On Settings app page, navigate to Accounts → Email Accounts page. Remove/Delete your old account (if you want completely remove from PC too);
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Open Microsoft Store again, Click profile icon → Sign In with your new account;
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Search MFS 2020, from search box or My Library Microsoft Store. Install MFS 2020;
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Move back Packages\Official\OneStore folder to original location;
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Run MSFS 2020. On package installation welcome screen, browse/choose your Packages folder location;
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MSFS 2020 will automatically check and download small KB files for a moment, and voila, finally landed on Main Menu.