Adding drop down filter control for Power Apps based on Choice column:

1. Add the formula in your apps "OnStart"

ClearCollect(YourCollectionName,Choices('SharepointList'.ColumnName))

2. Add to the Items property of your drop down.

YourCollection Name

3. Add the the Gallery's Items property tis formula

Filter(YourSharePointList,ColumnName.Value = Dropdown1.Selected.Value)

Add an "ALL" Value

1. Place the below formula in your Apps "OnStart" Property

ClearCollect(YourCollectionName, {Value: "All});

Collect
(YourCollectionName,Choices('SharepointList'.ColumnName))

2. Then add the "All" to the Gallery Item Property
If(Dropdown1.Selected.Value ="All", 'YourSharePointList', Filter('YourSharePointList',YourColumn.Value = Dropdown1.Selected.Value))

:)