You can't post direct links you get from youtube on your server to the users, they will get 403 most often if they use these links from different IP.

Heck, you even have the IP in the link itself :) 2605:a140:2236:8761::1

Also for protected media, like this one: https://www.youtube.com/watch?v=kJQP7kiw5Fk it only gives 360p and audio this way. Far from 4K you promise.

I was hesitant to open the link, thought it was a rick-roll. I've been working on the other downloaders, and I guess YouTube is one of the most used platforms, a lot of people are asking me to fix the youtube-downloader, I think I'll start working on that, thanks for bringing it up.

I use Firefox and I see (on the player's settings) that it goes as high as 1080. The addon of my InternetDownloadManager also goes as high as 1080.