I'm going through the documentation and this page about Face Expressions shows some code lines that give "deprecated API" warnings in Lens Studio. There's also one dead link "RenderMeshVisual"
https://developers.snap.com/lens-studio/features/ar-tracking/face/face-expressions

This API page indeed says that "getExpressionWeightByName" is deprecated, but it doesn't say what we should use instead.
https://developers.snap.com/lens-studio/api/lens-scripting/classes/Built-In.FaceRenderObjectProvider.html

However this one says nothing about it being deprecated:
https://developers.snap.com/lens-studio/api/lens-scripting/classes/Built-In.Expressions.html

It's a bit hard to know what to use.