@v-shimud
So the question would be - how functional would an App be with > 3 million records in it?
What I'm getting to is that the App should be an interface to information and subsets of information and not an "application" that is going to perform complex actions on large datasets.
So, there are certainly limits and some are able to be worked around - but, in many cases, it comes back to "why do you need so many records in a user interface?"
PowerApps is highly focused around lists and galleries of data - so the question would be, would you want your users scrolling through >3 million records in a list?
This is seen many times for large data sources where the concept is - need to search it all, but PowerApps does not do well with searching large sources.
So, the first think to look at is the DataSource...how much can you offset onto the server before it ever comes back to PowerApps.
For example - a large SQL database. We could pull down (with some effort) every row in the database in order to then successfuly search the entire database in PowerApps. But, perhaps the better method is to create a View or perform a function on the database and only have it return what is necessary/desired.
So...not sure if this helps in your design process, but it is something to consider.