The flatpak has been working for me on Linux Mint, although the flatpak didn’t work on Ubuntu proper. From what I understand the Mint devs do some extra tinkering to support flatpaks better than vanilla Ubuntu. Have you tried downloading the binary and running it from a terminal?
The Appimage also works well for me on my Ubuntu XFCE box.
I tried to find the video on PeerTube, from the end users perspective I think we should encourage others to choose community over corporate and use platforms like PeerTube to post these videos instead of YouTube (Alphabet).