You don't need to use the youtube-dl
ytuser:<youtube username> option. I was able to start downloading and download several videos from the channel that you linked to in your question without using that option, but my answer won't work on older versions of youtube-dl. I tested my answer on both an old and a new version of youtube-dl. It worked on the latest version of youtube-dl, but it didn't work on the old version.
Update youtube-dl to the latest version before you start downloading all the videos in a channel.
sudo snap install youtube-dl # start with snap run youtube-dl
sudo apt remove youtube-dl
sudo apt install python-pip
pip install --user youtube-dl
If you already have installed youtube-dl with pip, you can update it to the latest version with this command:
sudo pip install --upgrade youtube-dl # omit the sudo if installing in a Python virtual environment
Open the terminal and type:
youtube-dl -f best -ciw -o "%(title)s.%(ext)s" -v <url-of-channel>
<url-of-channel> is replaced by the URL of the channel and replace
FORMAT with any available video format, for example
18. To show the available formats of a video type:
youtube-dl -F <url-of-video>
Note: If you are downloading a lot of videos, you should change directories to the directory where you want to save the videos before you start downloading them.
-f, --format FORMAT
video format code
force resume of partially downloaded files
continue on download errors, for example to skip unavailable videos in a channel
do not overwrite files
print various debugging information