@Schloern
To run ros packages, it is necessary to run the setup.bash file, for example, the setup.bash file should be run in the linux operating system.
Start the QT Creator application in the terminal where you enter the setup.bash controls.
step 1: Open terminal and enter "source /opt/ros/humble/setup.bash" command. Note: this is ros humble enter your own setup.bash file
step 2: Open the QT Creator application from the terminal you included ros2
step 3: If you want to work simultaneously with ROS, use threads.