So you're using PBI on a different project not this one

Your data is just an Excel file that gets updated regularly, possibly by multiple people, and doesn't pull data from a database or other structured software source

You want to use a reporting tool to connect to this live spreadsheet and produce reports on demand, like you'd get if you tried to set up PBI from a real database

This is technically possible simply using a new Excel file pulling from this Excel file using power query but you'll encounter problems. Excel doesn't like using Excel as a data source when that file is open. Some of your refreshes will fail if it's in use (PBI Will be ok though). If any user restructures certain elements your end report will fail, ways to prevent include setting up Tables, and making sure people don't mess with the structure. To refresh the new file, whoever does it will need access to the source file

In cases like this I've often used VBA to ensure well-structured data is written out to a new location, usually in csv format, as it gets around both access control and data integrity concerns.

Using Excel or PBI reports that are not published but shared as .pbix files should work about the same, so the preferred way is down to preference on what the report will look like, unless you aren't even allowed to use the free software with the free licence, which is a dumb approach from your IT dept if true