This information is available using the REST API. In cases of seldom use, we can extract the information using only the browser. If you need this kind of listings often, it will be easier to to do via Illuminate.

First, we will log into the system as an administrator.

Then, in that same browser (for example, in a different tab), we will access this URL (obviously changing the initial part to point to our server):

https://MISERVIDOR.blackboard.com/learn/api/public/v1/users?
fields=externalId,userName,institutionRoleIds,name

The command will load on the screen information similar to this:

"externalId": "mi.alumno",
"userName": "mi.alumno",
"institutionRoleIds": [
"MATEMATICAS",
"BbMobile",
"STUDENT"
],
"name": {
"given": "Mi",
"family": "Alumno"
}
}

The list is paginated 100 at a time, so to access all users, we either have to reload adding &offset=NUMBER at the end of the URL or create a script that retrieves all pages automatically.
Example for the second page:

https://MISERVIDOR.blackboard.com/learn/api/public/v1/users?
fields=externalId,userName,institutionRoleIds,name&offset=100

It is also possible from the Bb Illuminate interface using a SQL query similar to the one proposed in this article