Yes you normally click / highlight on the word “calendar” ticked under the account “to show the calendar on the right” as in this Gmail calendar below. Same goes for any of your other account calendars.
If you “close the calendar” and “reopen the calendar” using the arrow on the left of your account, no calendar will be displayed on the right (until you click / highlight the word calendar again).
So if you always want to see your calendar when you re-open eM Client, make sure you “leave it clicked / highlighted” on the word calendar, (and don’t close the calendar via the dropdown left arrow).
Note:- Any other checked / ticked calendar menus like eg: Holidays etc, below each calendar will all show on the calendar at the top.