The calendar on the Samsung device usually shows all accounts that have been logged in, and the following calendar/accounts are available by default

The accounts cannot be completely removed from the calendar, they can only be hidden.

Android 10 (One UI 2.0)
Step 1:  Open the  Calendar -App
Step 2:  Open the  menu
Step 3:  Tap on desired  Account
Step 4:  Hide or Unhide the  Account
  1. Open the Calendar-App
  2. Open the menu
  3. Tap on desired Account
  4. Hide or Unhide the Account

Samsung Instructions