Hello,
You cannot delete the Inbox folder itself in Outlook, only the emails inside it. Open Deleted Items, select the emails, then move them back to Inbox. If Deleted Items was emptied, go to Tools, then Recover Deleted Items, and restore them from there. If emails now look separated, go to View, then Organize By, and set it to Date to return to the normal layout. If Recover Deleted Items is missing, confirm your account type in Outlook settings since this feature depends on Outlook.com or Exchange.