Need Advise on applying Dynamic RLS on Power BI dataset which is converted from SSAS tabular cube

1st Part of the Question:

It sounds like you're taking the right steps to convert your existing SSAS tabular cubes to a Power BI dataset, and including the USERPRINCIPALNAME() data is indeed a requirement for RLS to work in Power BI. However, it's possible that there may be other steps that need to be taken in order to ensure that the RLS rules are working correctly in Power BI. I would recommend double-checking that the Cloud settings are correctly set up for RLS in Power BI, and also reviewing the documentation for setting up RLS in Power BI to ensure that all necessary steps are taken.

2nd Part of the Question:

Regarding the challenge of applying RLS to a large volume of data, there are a few potential solutions that you can consider:

1. Data Sampling: You can import a sample of the data into Power BI Desktop and apply RLS on it, then test the security roles in the Power BI Service. If the RLS rules are working as expected, you can then apply the same roles to the full dataset.

2. DirectQuery with Parametrized RLS: Another option is to use DirectQuery and parametrized RLS. This allows you to pass the user information to the data source to perform the RLS calculation, instead of performing the calculation within Power BI.

3. Power BI Premium: If you have a large volume of data and need to apply RLS, you may consider using Power BI Premium. Power BI Premium provides more resources for data processing and allows for DirectQuery with RLS on large datasets.

I hope these suggestions help you achieve your goal of applying RLS to your Power BI dataset.