@Molly Myers - It seems like you are having trouble adding server administrators to your Azure Analysis Services servers using the Azure portal. I'm sorry to hear that.
Based on the information you provided, it seems like there might be an issue with the portal. However, before we jump to any conclusions, let's try to troubleshoot the issue.
First, can you please confirm that you have the necessary permissions to add server administrators? You need to be a server administrator or a member of the Azure Analysis Services Contributor role to add server administrators.
If you have the necessary permissions, can you please try adding the server administrators using a different browser or an incognito window? Sometimes, browser extensions or cache can cause issues with the portal.
If that doesn't work, can you please try adding the server administrators using PowerShell or REST API? You can find the instructions for using PowerShell and REST API in the documentation I provided below.
If none of these solutions work, please doshare the region of the Analysis services for further assistance.
For more details, refer to Analysis Services - Manage server administrators.
I hope this helps. Let me know if you have any other questions.