Can't compile

[Steven Friedrich]

I'm trying the exercise in An exercise for new contributors.

I've cloned the repository from GitHub, and opened  the project file 
CMakeLists.txt at the root of the source code.

I am unable to compile it, QtCreator says: No suitable kits found.

I had Desktop Qt 5.15.2 GCC 64 bit installed, and I added 5.9.9. Both 
are greyed out.

Is it restricted to 32 bit on Desktop?