I just got a brandnew S20 FE but having issue with taking Whatsapp call using controls on my steering wheel. It's connected to bluetooth fine as I'm able to take non-whatsapp calls just fine. Strange enough I can reject whatsapp calls but not taking them! It's few weeks and I have already regreted switching from Iphone to Samsung😩
Whatsapp calls are treated as media not gsm calls so the usual protocols do not work. You may get sound through the car speakers if you answer the call using the phone.
Thanks for your comment but, I had Iphone 7 for past 5-6 years and I could answer Whatsapp calls using controls on my steering wheel just fine. It seems this is where Samsung or Android in general falls short!