Per Twitter poll results, this week's Friday Functions video is demonstrating the GroupBy() function. Feel free to use grouped results in Drop Downs, List Boxes, and even Galleries (as long as the control can manage multiple items). I do the demonstration with an app connected to SharePoint, but I'm not using a custom form only because the business scenario requires a mobile application.
Note: Always preview your app to test when using Flexible Height Galleries as the template row will look taller in the canvas - and the preview will give you a better idea of what it will look like for your app consumers.
Check out more details about GroupBy and Ungroup in the reference link below.
https://docs.microsoft.com/en-us/powerapps/functions/function-groupby
Enjoy!
