Dropdowns on PowerApps are limited to displaying 500 items. While it makes sense it should have a limit of what can be displayed at a time and 500 seems reasonable to me, this will likely create problems as your application grows. An attribute to enable search and filter data using delegated queries when applicable would allow this control to be used with no concerns. If people don't want to use search they can just disable that. I know combo boxes do this already but on form controls you don't have the option to use a combo box.
So an an alternative would be to allow combo boxes to be used on form controls.
Note this has nothing to do with the limit to non delegable queries. The control itself is limited to 500 items and displays the message below as the last item displayed. The 500 item limit is also stated on the PowerApps documentation.