I suggest using the
SysInspire MBOX converter software to
Convert MBOX to PST. It can handle MBOX files from 25+ email clients, including AppleMail, OperaMail, PocoMail, and Thunderbird, among others. It can transform a single MBOX email or a group of MBOX emails into a PST file with no changes to the emails' layout, styles, email headers, or other elements. It works for all Windows versions up to 10 and MS Outlook 2019, 2016, 2013, 2010, 2007, and 2003.
Read More:- Import mbox file to office 365