This is neither helpful nor the resolution. My iOS is updated to the latest and WhatsApp too. It is not an issue with WhatsApp but iOS as it happens only in iPhone.
Instead of sending a generic response, I will suggest you try a replicate the issue after understanding what it is.
Try sharing a video on YouTube. You will see options like below (you must have both WhatsApp and WhatsApp Business installed) -

if you click on WhatsApp it will take you to WhatsApp Business first and then ask you if you want to share via WhatsApp instead.
The only way to avoid it is to scroll to the right and click on 3 dots (more) -

now you will get a different icon for WhatsApp and WhatsApp Business. So if you now select the WhatsApp button, it works fine -

Try it and then reply