For YouTube, go read this:
For JDownloader, that's pretty much off-topic here.
Meanwhile, here's some useful reference material:
https://groups.google.com/g/video-downloadhelper-q-and-a/c/BzPLK2YyL-sBe sure you carefully read the first 2 paragraphs there. Once you have read that, you can check out the references within that web page that I am about to give you. But don't just find the relevant link & click it. READ the context around the link. I recommend you bookmark that link & read the entire page, if not now, if not in one sitting, bit by bit over time.
You find a reference on that web page by searching the text of that page using various search keys. The search keys I am suggesting are these:
stealth quote
short tutorial
using gmail to post here
Next, look for "stealth quote" within the text of that web page. That will give you another link to click. Click that, read what you find, & follow the advice, not just for your posts in this thread, not just for your posts in this forum, but for your posts anywhere on Google Groups.
Next, look for "short tutorial" within the text of that web page. That explains why your response here will use the Reply all button. It also explains why you will NOT use the Reply to author button.
I see you are on GMail. It is important that you also search for "using gmail to post here" within the text of that web page. If you don't follow the advice in that reference, you will appear to be extremely rude. You don't want to be rude, do you?