I want to be able to call C# code from JavaScript. The mono project used to have a WASM SDK that you could download from their old Jenkins server, but that is no longer public. Existing docs tend to point toward those builds. The Azure Devops builds do not include this SDK. A few messages I've seen on their Github account indicate that they are now focusing on the .NET 6 for WASM. I do not wish to use the Blazor components. Is there a way in .NET 6 to build a minimally sized WASM binary without the Blazor UI?
Yes it's absolutely possible. Blazor does not have a monopoly on C#/WASM and it's far from clear that it's going to wind up being the best long term option (and a lot of evidence it's not).
I recommend starting with the Uno WASM Bootstrap. https://github.com/unoplatform/Uno.Wasm.Bootstrap
2022-06-30 Edit - More evidence Blazor is not the only game in town nor even at the forefront of innovation here: https://visualstudiomagazine.com/articles/2022/06/29/uno-platform-4-4.aspx