The process of building custom applications and tools that interact with Microsoft SharePoint, including SharePoint Online in Microsoft 365.
Based on your description, it sounds like you're looking for a cascading or dependent dropdown, where the available values in one column are filtered based on the selection made in another column.
SharePoint Online doesn't provide this behavior out of the box for standard Choice or Managed Metadata columns, and the available options may depend on how your library and columns are configured. One possible approach may involve using Lookup columns and additional customization with Power Apps, but the implementation details depend on your environment and requirements.
Since your question involves form customization and dependent dropdown behavior, you may get more targeted guidance from the Power Apps Community: Microsoft Power Platform Community Forum Thread
This forum is dedicated to Power Apps and SharePoint integrations, and it is actively monitored by Microsoft engineers, MVPs, and Power Platform professionals who are familiar with recent security changes and known platform limitations. You are more likely to receive confirmed guidance, workarounds, or information about known issues and roadmap updates there.
The reason for this redirection is that the Microsoft Q&A forum focuses mainly on general Microsoft 365 topics and has limited coverage for Power Apps–specific behaviors and regressions. The Power Platform Community is the best place to get timely and accurate insights for this type of issue, and your question may also help other users facing the same situation.
I’m truly sorry for any inconvenience this redirection may cause. My goal is to help you get the most accurate and helpful support possible, and in this case, the Power Platform Community is the most appropriate channel.
Thank you for your understanding. Have a nice day and stay healthy!
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