I want to replace the HDD in my laptop with an SSD. Then want to install a completely fresh Windows 10 Home (64bit). I will do an installation with a USB stick. There's an activated Windows 10 on the HDD. I read out the product key. Can I then use this key for Windows 10 on the SSD? Or do I have to delete the HDD beforehand so that the product key is "free" again?
No, you can use this key
But if you swap it offline, how will MS check the key?
The license is personal, not hardware.
If you have created an online account or have a Microsoft account, you do not need a key at all, simply log into the fresh Windows account, then the copy will be automatically licensed.
So for me it is currently in the Settings under the tab Activation: "Windows was activated by a digital license linked to your Microsoft account". So would the switch to the SSD work without problems with the activation?
Yes, if you create an online account (this is the standard setting in Windows 10), but you can also explicitly create an offline account, it would not be licensed.
The license was and is always related to devices. Only hardware change is ok. There's also no deactivation. That's why you can be e.g. Sell laptop with win without having to change anything, unless you have connected it to your ms account, then you have to remove it. License is for 1 device and not for 1 person.
This is recalculated with the hardware each time windows is started. If you change too much hardware, the activation goes out immediately.
That is simply wrong. With Windows 10 you acquire a digital license, it is account-linked.
The devices are only linked.
