Why does the vivoactive 3 dosn't count cardio point while i ride a bike...

What do you mean by cardio points?  Are you referring to intensity minutes? 

Yes, sorry... 

In the device settings on your Garmin Connect Mobile app, or Garmin Connect online, you'll be able to customize your heart rate zones for "standard", "running" and "cycling".  Depending on how advanced you are at cycling, the average person's cycling Max HR is 5-7 bpm lower than their running Max HR. Having the correct RHR is very important as it is used to calculate intensity minutes. I would check and make sure your zones are set correctly. Then remember, for intensity minutes to register you have to be doing moderate to vigorous exercise for 10 continuous minutes. (Usually zone 3 or higher). If you don't maintain 10 continuous minutes, the clock starts over. Otherwise you should be getting intensity minutes while cycling.  I hope this helps. 

Thank you, i will try your asvive... But... The watch does Not count intensity minutes even when i choose cycling and cycle for 30 minutes with a heartrate up to 160... 

One thing I forgot to mention.  On your computer open Garmin Connect.  Select your profile & account and open "account settings" on the far right.  On that page, select "user settings".  Make sure your "activity class" is set properly.  Select the blue circled "?" if you have questions on what class to select.  

I dont really know how to get a right activity class. I don't train that mich, most of my activity is walking and a bit of cycling 

Thank you very much! I will try These setting... Greatings from germany