If you're using a SharePoint list in a Power App and some data is missing, you can change the data row limit to a higher number in the Power App settings. See how this works here.
In the Power Apps editor, open menu File and Settings.
In the General section, scroll down to the "Data row limit" and modify the number how many items shall be retrieved from the data source.
Depending on the data source connector, the value can be set. The default value for SharePoint custom lists is 500 items. You can increase the setting up to 2000 items as in the screenshot. Find more about the data row limit and possible workarounds here:
I hope this quick tip helps as a quick fix for scenarios where the 500 item limit applies.