Export to excel for large data set which is to be retrieved from 2 data entities

As others have said, combining the two queries into a view could be the simplest way to retrieve all the data from the 2 entities (may be able to suggest more if knew what the structure/data to be retrieved from the entities were).

As far as using the Export to Excel functionality, you may be able to get over the limitation of query entities by pulling the dataset in batches (e.g. pull 500 records at a time), assign the records to a process variable and increase the increment each time until the dataset is complete. This approach may run into issues depending how big or efficient the view you'd pull from would be, but you would have access to all the data from both entities if you can accomplish that.

As others have said, combining the two queries into a view could be the simplest way to retrieve all the data from the 2 entities (may be able to suggest more if knew what the structure/data to be retrieved from the entities were).

As far as using the Export to Excel functionality, you may be able to get over the limitation of query entities by pulling the dataset in batches (e.g. pull 500 records at a time), assign the records to a process variable and increase the increment each time until the dataset is complete. This approach may run into issues depending how big or efficient the view you'd pull from would be, but you would have access to all the data from both entities if you can accomplish that.