Why do I get the error "Unsafe code may only appear if compiling with /unsafe"?

To use unsafe code blocks, the project has to be compiled with the /unsafe switch on.

Open the properties for the project, go to the Build tab and check the Allow unsafe code checkbox.

Probably because you're using unsafe code.

Are you doing something with pointers or unmanaged assemblies somewhere?

Search your code for unsafe blocks or statements. These are only valid is compiled with /unsafe.

For everybody who uses Rider you have to select your project>Right Click>Properties>Configurations Then select Debug and Release and check "Allow unsafe code" for both.