Self-hosted version 20.13.1633.7620
After enabling and testing SAML w/ Azure AD, I disabled internal authentication. Once I did that I was completely locked out of the server, and clicking the Login button on the main page resulted in a 404 error. I tried resetting the installation and configuring a new default Administrator account, but doing so did not re-enable internal authentication as expected so I still couldn't log in.
Support showed me how to edit the web.config file to re-enable internal authentication in order to log in with the default administrator account. Search web.config for "user.xml" and change the "enabled" value to true.
After re-enabling internal authentication, Azure SSO started working as well. It appears that disabling internal authentication prevents SSO from working, so for now I have to keep internal authentication enabled even though we want to use SSO exclusively.
Customer support service by UserEcho