Inspiron 5400 AIO Windows 11 Pro Disk 0 (C:) Active time 100% for several minutes

If your system boot drive is a spinning hard drive, that would be part of the reason.  Low system memory is another part of the reason. 

To solve problem, upgrade to solid state drive, upgrade to 16 GB of memory.  Check the Startup Apps in Task Manager and disable all unneeded apps can also speed up the boot process.

@Chino de Oro​ Thank you very much, but what happen with my Windows 11 software. My activation state is Active if I upgrade my HDD to SSD ???.

Thanks.

It sounds like you just confirmed the reason for the busy boot time.  Then upgrading the HDD to an SSD will be a good solution to resolve your issue. 

There are several ways to upgrade, you can clone the old HDD to the new SSD, you can create a backup drive image of the HDD then restore it back to the SSD, or you can perform a clean install of operating system (a preferred method), and reinstalling of needed apps to the new SSD, then restore data from backup.  A clean install can get rid of old remnants, patches, and unneeded bloatware.

Whichever the methods, the Windows license is embedded on the motherboard and will be activated again on any new SSD.  There is no need to worry about that.

Excellent. Thank you very much. I really appreciate your help.

Best Regards