I figured out what have I done, but my example wouldn't help anyone and I'd be ashamed to type it here as because it was quite noobish, so I'm marking as solved.

Yes, I did.

I downloaded 15 GB of files to empty Driver and deleted it days after.
My Driver says there is still 15 GB of used space, while there's no visible or hidden files. But I used Recuva to reach those...

Sorry if title is misleading or somehow not right, but I really don't know how to explain this properly.

The problem is that my audio has completely changed days ago. Notifications from programs...

I've just did that now. In Registry Editor it says that "Startup" is at:
%UserProfile%\AppData\Roaming\Microsoft\Windows\Start Menu\Programs\StartUp which is correct location I think.
If I...

I can find "Sheel Folders", but I don't understand how to activate this "/v" thing you wrote up there. I tried to find a way online, but I don't know how to search for it.

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I tried couple names already, such as Startup, Windows Startup, Startup folder and Start up. It doesn't seem to be able to make startup tab work and let me add more programs there.

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Microsoft Windows version 1909(OS Build 18363.719)

I opened Start Menu and deleted folder "Startup", which is supposed to be in:
\User\Appdata\Roaming\Microsoft\Windows\Start Menu\Programs\ ...