Calendar and Appts Wiped Out by Update

I understand that you are experiencing a frustrating situation with your Calendar app on Windows 10 Pro. I'm here to assist you in resolving this issue.
Firstly, it seems that your Calendar app was replaced by Outlook when you launched it after a recent Windows update. This might have happened due to a default app association change or a setting that switched your preferred calendar to Outlook.
To retrieve your appointments that were previously entered into the Calendar app, you can try these steps:
1. Open the Outlook app and check if your appointments are present there. Sometimes, the transition from the Calendar app to Outlook may have moved your data.
2. If you don't have any luck in Outlook, you can try recovering your calendar data from a previous backup if you have one. Look for any backup files or restore points that were created before the update, and see if you can restore your calendar data from there.
3. In case you were using a Microsoft account to sync your calendar, you can also try accessing your Microsoft account online (at outlook.live.com/calendar) to check if your appointments are still available there.
As for reverting back to the previous Calendar app and removing the Outlook/Google setup, unfortunately, it is not possible to revert to previous versions of built-in Windows apps like Calendar. However, if you prefer using the standalone Calendar app rather than Outlook, you can try setting it as your default calendar app by following these steps:
1. Open the Settings app by clicking on the Start button and selecting the gear icon.
2. In the Settings window, click on "Apps" and then select "Default apps" from the left sidebar.
3. Scroll down and find the section where it says "Choose default apps by protocol." Look for "webcal" and click on the default app (in this case, Outlook) next to it.
4. A dropdown list will appear with available apps. Choose the Calendar app from this list.
By doing this, you should be able to use the standalone Calendar app again for your appointments.
I hope this information helps you retrieve your appointments and make the necessary changes to your calendar setup. If you have any further questions or need more assistance, please let me know!