@Demerit is correct - and I'll also leave the Drupal portion of the question unanswered here. There are modules that might have bugs in newer versions, or aren't compatible with Drupal 8.8.x.
As for CiviCRM, you shouldn't see meaningful changes to existing functionality with an upgrade from 5.17 - that's only a few months back. However, it's always good to test key functionality in case a bug snuck in - doubly true if you're using custom extensions or similar. Also when upgrade completes, you'll see a list of potential changes you'll need to investigate. For instance, I'm pretty sure that some receipt templates have changed. If you haven't customized your receipt templates this shouldn't result in a meaningful change, but you may be missing out on some of the new functionality if you've customized and don't review the changes.