How to build, deploy and execute dotnet library on Heroku
Yes, heroku dyno is a standard ubuntu (18.04 - 20.04 it depends on stack).Our team used own buildpack and own build script.
HVG/self-buildpack:https://github.com/HVG/self-buildpack
Sample Asp.Net Core project:https://gist.github.com/felegy/8834d26063204d129a7b2893a91f6627