What are special characters?
Special characters are characters outside of the typical keyboard options.
In the realm of Blackboard, these characters can be split into two categories: math and language.
Math characters
Blackboard's content editor has a built-in Math editor, which can be used to type in math formulas and special characters.
Math Editor
The math editor can be accessed by clicking the plus sign in the content editor, then selecting Math.
Note: The Math Editor isn't available in the + sign menu of the content editor when creating Announcements or using Messages, but it is available when creating assignments or assessments or giving feedback.
Learn more about the math editor in Blackboard from Anthology's support page:
Language characters
The content editor in Blackboard does not have it's own special language characters option. To add characters such as é and ü, utilize the operating system pop-up menus. There are keyboard shortcuts for these menus on Windows and Mac computers.

Windows
Windows + . (period)
Hold down the (Windows) key and press . (period) and you will see a menu. You can search for and select the symbol you need.

Learn more from Microsoft:
Mac
Ctrl +Cmd + Spacebar
To bring up a similar menu on Mac, hold down Control + Command + Spacebar. You can type in the search bar to narrow the list, and select the symbol you need.

Alternatively, you can hold down any vowel (including y) on your keyboard, and options will pop up e

Learn more from Apple: