Hi @Waleed Ahmad ,
Based on my knowledge, "This Computer Only" appears when the outlook has been configured with IMAP.
Please try the below,
- Configure a new outlook profile with MAPI and with cached mode enabled
- Once profile is configured, go to system tray -> outlook -> press ctrl+right click on outlook icon -> click on "Connection Status" to confirm the connectivity
- Use the same method as step 2 and click on "Test email autoconfiguration" -> uncheck "use guessmart" and "secure guessmart authentication" and click on "Test"
- Check if the OAB URL has been retireved
- Go to File -> Account settings -> Download address book and click on "Ok"
- Verify the Address book
If still having issue, check the Address book in Exchange 2019,
To verify the system mailbox,
Procedures for offline address books in Exchange Server
If the above suggestion helps, please click on "Accept Answer" and upvote it