I reviewed the docs (https://learn.microsoft.com/en-us/aspnet/core/blazor/components/render-modes?view=aspnetcore-9.0#apply-a-render-mode-to-the-entire-app) and apparently had to add @rendermode="InteractiveServer" to the Routes and HeadOutlet elements in App.razor. I'm not entirely sure why this fixed it since my .razor was already using @rendermode InteractiveServer locally. Perhaps the rendermode needed to be set globally like that to support MudBlazor's components too? Not sure.