Hi @Pankaj Bhakta ,
Welcome to our forum!
Are you currently running only Microsoft 365 and have removed office 2013? If so, what's the version of your Outlook? (File > Office Account > About Outlook). Please make sure you have upgraded your Outlook to the latest version.
And what's the type of your account(POP/IMAP/Exchange)?
For the two calendars with the same name you mentioned, did this issue occur after outlook upgrade? As I know, if you only upgrade outlook, the display of calendar won't be affected. Have you done any other special operations?
If your account is an Exchange account, please log in to web mail to check whether two calendars with the same name will be displayed. If the same is true on web mail, please export the two calendars to backup on the outlook client. Then create a new profile(control panel>mail>show profile>new) and reconfigure your account, merge the two calendars into the one calendar you need to keep, and then delete the one you don't need.
If you are configuring pop and IMAP accounts, please back them up first and then merge them in the new profile.
Hope to help you! If your issue has any update, please feel free to post back.
If the response is helpful, please click "Accept Answer" and upvote it.
Note: Please follow the steps in our documentation to enable e-mail notifications if you want to receive the related email notification for this thread.