Is it possible to reference a c# class library in an Azure Function visual studio project?
I am aware of the possibilities to reference external libraries and Nuget
Currently, project references are not supported, but you can have the output of your project (the resulting assembly and possible dependencies) copied onto a folder under your function's root, which you can then leverage using the external libraries support you've mentioned above (e.g. #r "..\myassemblyfolder\MyAssembly.dll")
If possible, I'd suggest opening an issue with that feature request, sharing more about your scenario on this repository. This allows other people to upvote those requests and helps the team prioritize this work.