Actually, a native way of allowing user inputs to your Power BI report as what-if scenarios or manual overrides is embedding Power Apps directly into the report. While native Power BI visuals wouldn't allow direct data entry, Power Apps offers users a really seamless way to input values that can be written back to a database and refer dynamically to values associated with your visuals and DAX logic.
Here's how to go about it:
Embed a Power Apps Visual: Add the Power Apps visual from the Visualizations pane and connect it to the table that holds user input fields. Use Power Apps Studio to design a form or interface for user entry. Store and Read inputs in the app to save inputs to a connected data source (e.g., SharePoint, Dataverse, SQL). Then, use a scheduled or manual data refresh, using DirectQuery mode if supported, to bring input back into Power BI for measures and filters.
Use DAX to Incorporate Inputs: When the input data are available in your model, design DAX measures to model user values into your dynamic KPI, visuals, or what-if scenarios.
This will bring a level of interaction much more than Power BI usually embraces in a secure, scalable environment. It is perfect for budgeting for, recasting, or user-driven simulation cases.