A slow Windows could be many reasons from software to hardware, as you tried reinstalling Windows 10 so I believe its not your Windows or software related issue. Try to scan your hard drive for any bad sectors use this software (hdsentinel), download it from google, its free and if it shows your hard disk health low than you have to change your hard drive to a healthy one and install Windows 10 in it. Hope it helps for further questions feel free to ask.
My Laptop Windows is very Slow
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