Assuming you are using Raspbian buster (32 bit)
Please refer to
https://github.com/TheGameCreators/AGKTier2/wiki/How-to-compile-AppGameKit-Tier2-libraries
1) Download AppGameKit 2021.02.10 (Raspberry Pi) (168.74MB) from your account. - unzip to a location of your choice.
2) git clone https://github.com/TheGameCreators/AGKTier2
3) Download GLFW - git clone https://github.com/glfw/glfw
4) If you don't have doxygen installed - sudo apt-get install doxygen
cd glfw
mkdir build
cd build
cmake ..
make
make install
5) cd AGKTier2
I stated that I experienced a green overlay due to a shader issue.
If you change line 1841 in AGKShader.cpp (AGKTier2/common/Source) from
colorVarying = color; to colorVarying = vec4(1.0, 1.0, 1.0, 1.0);
that seems to solve the issue.
6) make
7) cd apps/interpreter_linux
8) make
If successful you should see a folder called 'build' with LinuxPlayer32, rename LinuxPlayer32 to PiPlayer,
then replace the Tier1 PiPlayer found in Tier1/Compiler/interpreters with your new PiPlayer.
Hopefully the instructions will help you get AppGameKit working on the RPI4.