How to reset Mac OS iCal - Apple Calendar

Due to migrating and upgrading on mac os since some time I was facing calendar issues:
- "The URL https://<...>/ encountered HTTP error 302. Make sure the URL is correct."
- some calender subscriptions disappeared. I could not create subscriptions: "... this calender exists."

Important to mention: I had no local calender entries!

So I wanted to reset my iCal in Mac OS.

The following is a description, how I have done this.
No garantee!

MAC OS X Yosemite Version 10.10.2 - MacBook Pro - iCal Version 8.0 (2021.6.1)

1. Take a note of your calender seetings
    - open system settings - internet accounts
    - make a note or screenshot of your settings. You need it later, when you setup.
    - in calender do a right click on calender subscriptions and make note of the URLs

2. Disconnect all your attached devices
    - disconnect mouse, keyboard, disk drives etc.

3. Disconnect from Network
    - disconnect network cable
    - disable WI-FI
 
4. Close all Applications and Reboot

5. Close all applications started due to autostart operations

6. Remove calender account
    - open system settings - internet accounts
    - remove the calender account

7. Remove Caches and Calender data
    - open a finder
    - from the menue select "connect to folder":
       /Volumes//Users//Library
      where is the name of your disk, ans is your user.


    Important! Do not delete anything. Simply move the following folders to a new location
    (for example your desktop) to have a backup!

    - in the above mentioned folder ".../Library" move the following folders to the backup location:
      1. Caches
      2. Calendars
    - check the folder are no longer under ".../Library".
    - now goto folder   ".../Library/Containers" and move the following files to your backup location:
      3. com.apple.CalendarAgent
      4. com.apple.iCal
    - check the files are no longer under ".../Library/Containers".

8. Reboot again

9. Open iCal
    iCal should be reset to defaults.
    Re-create your iCal account and subscriptions.

10. Your calender should be fresh and fast.
      Remember to clean up your backed-up folders.