Export Apple Mail to Microsoft Outlook has an additional challenge because it is a migration not just from one email client to other, but also from one OS (Mac) to other (Windows). Therefore, it can get very tricky to move the data from Apple Mail to Outlook without a professional assistance.
You can’t directly import Olm file to Mac Mail because it is not supported. Mac Mail uses Mbox file to store your data, and Olm file is only for Mac Outlook. There are other ways to make the transfer of contents, such as drag your folders to desktop and it will convert the files to Mbox automatically.