It would be easier if you manage to make a video of it. π₯
What I can understand from your written feedback is that the BLUE PITCH SWITCH is hard to react:
Keep pressing long enough until you see the VERTICAL INDICATOR ARROW (on the black gauge mixed with TCAS) actually moving down, THEN you may expect the aircraft to pitch down.
It is very slow to react, be patient while pressing the BLUE PITCH SWITCH.
You can not expect the autopilot to be as sophisticated as a 737...
to ensure a good sequence and a good activation of the autopilot follow the NORMAL TAKE-OFF FLOW:
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You can activate the autopilot when you want, but remember:
if your aircraft isn't stabilized, the autopilot will not do it for you.
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If you were in IAS MODE then you switch to PITCH MODE on autopilot console:
it will be easier, BUT you will still have to press long enough on the BLUE PITCH SWITCH
Let me know if that help π