On some boards there are restrictions on what new members can post, particularly URL links and videos. As you only registered on this board a few days ago, I suspect this may be the reason for the lack of a video posting button on your toolbar. Wait a while, and see if it appears.

If it doesn't apppear, you could try contacting the board administrator:

https://community.ebay.co.uk/t5/Meet-the-Community-team/About-us/m-p/4779710

I see you are in Australia. Does the video icon appear for you on the Australian board?

https://community.ebay.com.au/t5/Community-Spirit/bd-p/2500000007