@ajit1>> In case you are using Firefox as your browser , you might consider the below addon
*addons.mozilla.org/en-US/firefox/addon/video-downloadhelper/
+1, I use it on Firefox for Linux. Works great.
Use Firefox Extensions to download the videos but if you want a third party software then I would recommend Portable Youtube Downloader. I have been using it for many years at places where I am not on my PC and it works just fine.![]()