A PC with a new installation of Windows can often appear slow in many ways for the first week or two of its use because it takes about that long (if not for much longer) for the multitude of updates that Windows demands to be downloaded and installed. Since some elements of the updates can't be installed when Windows is actually running, the actual updating process often only starts to occur when the machine is instructed to shut down.
So my guess is that the delay in shutting down is related to countless Windows updates trying to install themselves, meaning that the problem will eventually disappear of its own accord once everything is fully up-to-date.
and if you bought one of the newer ssd drives rather than an old mechanical ones, you will notice a speed increase, especially on boot start up etc and opening windows explorer, moving files opening browser..
Not just slow to shut down. I have just installed O&O safe erase, it open immediately but fails to start to scan for about three minutes. I checked Microsoft updates and none are downloading or running.
Go into Task Manager, click on 'Processes' and enable 'Show processes from all user'. Take a look to see if there's anything unusual there. (If one of the multitude of instances of 'svchost.exe' seems to be taking up a lot of resources, as often happens, right-click on it and select 'Go to Service(s)' to see what's actually behind it).
Don’t forget to load the motherboard drivers – I did this once on a new PC supplied with no operating system software, and wondered why I had connectivity problems etc.