Hm, the captcha worked on my end without issue and I was able to watch with audio.

I tested it just now with Freetube instead (should be available in most linux repositories), and that appears to work well for me without any captcha. Hopefully it should allow you to watch it without as many issues.

I don't see a way to download the video from within Freetube. I suppose a much more inconvenient but guarenteed method of capturing the video would be to capture it live by recording the video and audio in OBS.