I could be wrong, but you mentioned "Reinstall Windows 10 & Long Story", so I was wondering if maybe you didn't use the Windows 10 reinstall feature? Not system restore, the reinstall, or refresh feature?
If you did and have been using Windows 10 for a while then using the reinstall version that way may have reverted your PC to an earlier version of Windows 10 and since doing so then it is updating that version of Windows 10 to the current version since it has been a while causing your PC to slow down while trying to download or do other things.
That's a wild guess, I've had Windows updates cause problems using the PC and downloading in the past. So I thought I would mention it in case it is relevant to your situation.
Check in the Windows 10 Updates & Security, it may show you depending on what version of Windows 10 you started with as to whether it may or may not be downloading or installing updates.
Either way, I hope you get it worked out. Good luck!
Happy Holidays!
Bobby