-> The case when you disconnect your transmitter:
When you calibrate your transmitter, the center signal of the sticks is the new center. This signal does not have to be zero. As long as the transmitter is connected, the calibrated control signal is then zero. If you have not connected your radio and started the simulator, the signal will be 0 because there is no input. That is why you have a drift in these situation.

If you haven't connected your transmitter, you should choose a different input device. Open the menu with esc, go to Settings > Input Device and select another input device for which you have not calibrated anything. Then you can control the model from the keyboard without having a drift.

-> Maybe this is your question?
Have you calibrated your transmitter? Open the menu with esc and go to Settings > Input Device > Result. Look at the Result column. When you center your sticks everything should be zero. If not, you should calibrate your transmitter under Settings > Input Device > Model. There, click on Start Calibration and follow the instructions.

-> General info:
Of course, a helicopter always has to be controlled ... also in reality. Otherwise it will crash. There is also a continuous sideways drift caused by tail rotor force ... usually to the left as you see the helicopter from behind.

Yeah, that's real. The forward drift depends on the model, as many models are tilted forward by about 4°. So when you leave the ground, you have to tilt it back a little first. To prevent sideways drift to the left, turn the helicopter very slightly to the right ... so it flies at an angle. Only then will the helicopter not fly away.

In fact, you have to pilot a helicopter all the time, even if you're hovering in place