I can't speak to Blackboard from an overall ease of accessibility perspective, but I have had to train a couple of my previous clients who were graduate students to navigate it. All were successful using a modern browser, which means not Internet Explorer. Obviously, there are parts of Blackboard, or any complex system, that I never needed to get into with either client.
If memory serves one was using Firefox and the other Chrome.
Brian - Windows 10 Pro, 64-Bit, Version 1909, Build 18363
Tolerance is the positive and cordial effort to understand another's beliefs, practices, and habits without necessarily sharing or accepting them.
~ Joshua Liebman