Could you please share a bit more about the People Picker field that you mentioned? Is it a Person type column in your SP list data source?
Further, do you want to filter the People Picker Drop down, and only display 5 specific users within it?
I have made a test on my side, if you want to filter the People Picker Drop down, and only display 5 specific users within it, I afraid that there is no way to achieve your needs in PowerApps currently.
If you would like this feature to be added in PowerApps, please submit an idea to PowerApps Ideas Forum:
I think you can add an Outlook 365 group. Update this list to what you want, then you dont need to dig into your code to update people. You just update the group. Then, use the group for items.
I'll update this in a bit for the specifics. Ping me if this doesnt get updated in a day or two.
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