Is it necessary to add a product video during PH launch?

It's not necessary but helps a lot! Sweet spot is something around 30 - 90 seconds. Looms work great for this if you don't have a large team or are short on time. You can give your launch a personal touch by pitching your product and walking a bit through the different functionality.

yes it is, user can understand the product easily and quickly.

Video content is much easy to understand

no, but it does help significantly more.

I would recommend it 100%! I am a complete newbie at it and started working on the video script with PowerPoint by importing free stock images. Each slide was meant to describe what I wanted to display in a future video. Then when I was done, I went on Fiverr and look at a video explainer service! You can have a look at my videos (English/French) at dghfrance.com I plan to remake some of the slides but the idea is there! Hope it helps ;D

I will say yes. Easier to understand and save your audience time.

It's a good idea to use video introducing a product.

Yes, it helps. Think about it as an useful content for you to reach more people. It will be helpful after the launch as well. Btw, you can check out Wavel AI, we help you get more views with multilingual video translation