Hi, good day! I'm Jerico T., I understand that you're having some issues right now, I'll do my best to help you with your concern.

The Clean Boot is the best way to close or disable applications/programs that are less needed for your computer to startup. Rest assured that it's safe and you don't have to reset your device, you just have to restart it.

Closing or disabling programs one by one might be risky because you might disable important background processes. You may refer to the link below for the complete definition of Clean Boot and for the step-by-step instructions on how to perform Clean Boot.

https://support.microsoft.com/en-us/topic/how-t...

Please do let me know if you need any further assistance.

Hope this help. Have a good day.

Thank you,

Jerico T.

Store probably runs for doing automatic update check.

To turn it off, go to Start -> Settings -> Privacy -> Background apps and set it to Off.
More info in the article: How to Turn On or Off Background Apps in Windows 10.

You might also in this case turn off automatically-applied updates by going to
Settings -> Update & Security -> Advanced options
and set "Choose how updates are installed", to "Notify to schedule restart."

For the calculator :

I believe that this Modern app is among those that Windows 10 tends to keep in memory if used once. It probably runs in suspended mode, using very little memory, ready to be launched quickly when called, which is more useful in a tablet than a computer.

Windows might forget about it if you kill it off a few times using the Task Manager before shutting down. If this works, I advise in the future to use a third-party calculator instead of the Modern one, or it will come back.