Video Taken in Landscape Mode Doesn't Display Properly

Using my Pixel 7 Pro camera I made a video while using WhatsApp. I started out with the camera in the portrait mode. During the video I turned the camera 90 degrees to the landscape mode for about 15 seconds. Next, I turned the camera back to the portrait mode, said a few words, and sent the message.

When I reviewed the video, again I started out by holding the camera in the portrait mode. When it displayed the part I made in the landscape mode, this is how it looked:

So I turned the camera 90 degrees to the landscape mode and this is how it looked:

What's happening here - is this a WhatsApp thing?

I fiddled around with this problem a bit. Apparently if I put the phone in the landscape mode and then make my video call, the recipient will see the video in the landscape mode if he/she turns the phone to the landscape mode. But if I start the video chat in the portrait mode and then turn the phone 90 degrees, what is shown in my first post is what the recipient will see.

I hope this helps someone who has the same question.