libmono-2.0-dev 6.8.0.105+dfsg-1 (amd64 binary) in ubuntu focal

 Header files and static libraries for libmono-2.0.
 .
 Mono is a platform for running and developing applications based on the
 ECMA/ISO Standards. Mono is an open source effort led by Xamarin.
 Mono provides a complete CLR (Common Language Runtime) including compiler and
 runtime, which can produce and execute CIL (Common Intermediate Language)
 bytecode (aka assemblies), and a class library.