Open Invoices
Multi-select/ Select all the invoices you like to print or download
On selection, you will see more options that are available in Pink buttons.
Click on Mark as Sent
Please watch below GIF image to follow the steps:

Open Invoices
Multi-select/ Select all the invoices you like to print or download
On selection, you will see more options that are available in Pink buttons.
Click on Mark as Sent