Specifically, there are multiple ways through which you can bulk import MBOX files into Office 365, including free solutions. That is why users use intermediate tools like Thunderbird or Apple Mail. We will also try to convert MBOX data into Office 365 accounts by converting formats like MBOX to PST and EML, while admin-level users also use Azure AzCopy, which is a reliable solution. However, it is highly technical.
The best way that lets you import MBOX files into Office 365 user accounts is by using RecoveryTools MBOX to Office 365 Migration Tool, as it is designed both for home users and admin-level users. It also has an IMAP admin option that lets you transfer MBOX to multiple user accounts at once. Apart from that, it can easily handle bulk data at once. It has a simple graphical user interface that does not require any technical knowledge and makes the process easy.
https://www.recoverytools.com/blog/free-methods-to-import-mbox-to-office-365/