How to track pbi report modification in service

Hi. There is no way to go that deep at service. You can track operations activities at Service like a report was published, viewed, refreshed, etc. You can use the Admin workspace to check the activities or the API: https://learn.microsoft.com/en-us/rest/api/power-bi/admin/get-activity-events

If you want to track any change inside a report, the only way I can think about is developing with Power Bi saved as Project (pbip files decompresion) and save it in a repository (github or azure devops). That way a git repo will show you each change that was made. Using TMDL or TMSL for the files is the same, both ways will let you check the commits to the repo to analyze the changes.

I hope that helps