Add a hyperlink to the space navigation. You can link to internal or external web pages. Enter the Tab name and Tab URL. Upload or choose an icon. Then click Save.
How can I download a CSV file of users' roles within each space?
The fourth screenshot of Download CSV File of Users indicates that this is a current feature.
The fourth screen shot is showing the results of the CSV file after you import it into Excel.
There is not a way to download a list of users from a space based on specific roles only.
The CSV file will contain all the users of your site, you can import this into a spreadsheet program like Excel and then use the spreadsheets sort and filter tools to drill down to the information you are looking for.
The fourth screenshot clearly shows headings for spaces and user roles in rows:
Check out Membership Report
Choose a location