That's the nature of the beast.  Intuit Link has a very simple UI.  At the same time, it lacks the finesse and sophistication you'd find in more developed client portals.

In case your clients are not familiar with the operation of Intuit Link, including a link to the instructional video in your invite to them as sort of an onboarding tool may have relieve you of some of the time you may otherwise have to spend answering related questions: https://accountants.intuit.com/tax-client-portal-for-accountants/client-invitation/?wvideo=i4e9xhdwo...

If your client prefers written instructions, this article has almost exactly the same content: https://accountants.intuit.com/support/en-us/help-article/certified-public-accountant/intuit-link-ex...

For more specific questions about the use of Intuit Link, you can also refer your clients to the this article.  I have, however, bookmarked the section relating to the upload of multiple documents since that seems to be your pain point: https://accountants.intuit.com/support/en-us/help-article/import-export-data-files/taxpayers-use-int...