Could you please tell me more details about your report, such as the data source, connection mode, etc.? When you download your report from Power BI service, there are some considerations and limitations that you need to notice for they may restrict your download.
If your administrator has turned off the ability to download data, this feature won't be visible in the Power BI service.
You can download a file in either Reading view or Editing view. You must be at least a Contributor to the workspace that the report is in. If the report is based on a dataset in another workspace, you need to be at least a Contributor to that workspace as well.
If you create a Power BI report based on a dataset in one workspace and publish the report to a different workspace, you can't download the report if the dataset is configured for large models, incremental refresh, or has been modified by using the XMLA endpoint.
Datasets modified by using the XMLA endpoint can't be downloaded to a .pbix file.
Downloading a .pbix file that is larger than 1 GB isn't supported.
Datasets with automatic aggregations enabled can't be downloaded to a .pbix file. You must disable automatic aggregations training in the dataset settings and delete the aggregations tables by selecting the checkbox Delete automatic aggregations tables.