I’m not sure why IT would be going all way back to March 2019. Maybe you can download older versions of Power BI to your laptop/desktop so you can view them.
I also found that older version file extension is this: i just did a google search: " file extension for previous version of power bi"
The file extensions (PBIX and PBIT) are already associated with whatever version of desktop is installed and registered with Windows. The remedy is quite simple… just reinstall the latest version of Power BI Desktop and perform a Repair if you already have that version installed.’’
You will likely lose all the new formats, functions that you created in the updated version of power bi.
I also noticed that you can save the file in PBIT (older version) in the current version of power bi when you click on the down arrow on Save as type: Marked in yellow.
Check it out maybe it would work.
I would definitely encourage your IT area not to go back that far.
I hope this helps.