SOLVED.
The emergency stop button was stuck, which is connected to TinyG’ reset. Duhhhh 😛 :P.
Now it works fine.
CoolTerm does connect to TinyG. (https://github.com/synthetos/TinyG/wiki/Connecting-TinyG) No, not talking :(.
FYI this is the same machine as mine CNC 3040 –> https://www.youtube.com/watch?v=42ew5xjIBWM.