There are paid for converters. I never chose to use one. I ended up keeping Thunderbird on the machine for searching archives and used outlook for new mail.I was trying to import my data files from Thunderbird email clients to Outlook. However, I have faced a lot of issues in doing this. Can anyone suggest to me a proper way to import my files to Outlook 2019?
Here's an article that covers several ways of accomplishing the task. None of them are painless or quick.
https://www.stellarinfo.com/article/migrate-from-thunderbird-to-outlook.php
As advised above it's better to keep what you have in Thunderbird as reference and just start fresh with Outlook.