$ brew install youtube-dl
Warning: You are using macOS 11.
We (and Apple) do not provide support for this old version.
It is expected behaviour that some formulae will fail to build in this old version.
It is expected behaviour that Homebrew will be buggy and slow.
Do not create any issues about this on Homebrew's GitHub repositories.
Do not create any issues even if you think this message is unrelated.
Any opened issues will be immediately closed without response.
Do not ask for help from Homebrew or its maintainers on social media.
You may ask for help in Homebrew's discussions but are unlikely to receive a response.
Try to figure out the problem yourself and submit a fix as a pull request.
We will review it but may or may not accept it.

Warning: youtube-dl has been deprecated because it has a failing test since forever and no new release since 2021!
==> Fetching youtube-dl
==> Downloading https://raw.githubusercontent.com/Homebrew/homebrew-core/9a3e6f2
Already downloaded: /Users/sunyou/Library/Caches/Homebrew/downloads/d23bc8a1d41df94dfd988097b6b445c99400554c9b0c884f909c3318ed38122a--youtube-dl.rb
==> Downloading https://github.com/ytdl-org/youtube-dl/commit/aaed4884ed9954b8b6
######################################################################### 100.0%
==> Downloading https://files.pythonhosted.org/packages/01/4f/ab0d0806f4d818168d
######################################################################### 100.0%
==> Patching
==> Applying aaed4884ed9954b8b69c3ca5254418ec578ed0b9.patch
patching file youtube_dl/extractor/youtube.py
Hunk #1 succeeded at 252 (offset -8 lines).
==> python3.12 -m venv --system-site-packages --without-pip /usr/local/Cellar/yo
==> python3.12 -m pip --python=/usr/local/Cellar/youtube-dl/2021.12.17/libexec/b
==> Caveats
The current youtube-dl version has many unresolved issues.
Upstream have not tagged a new release since 2021.

Please use yt-dlp instead.

Bash completion has been installed to:
/usr/local/etc/bash_completion.d
==> Summary
🍺 /usr/local/Cellar/youtube-dl/2021.12.17: 845 files, 5.8MB, built in 1 minute 9 seconds
==> Running brew cleanup youtube-dl...
Disable this behaviour by setting HOMEBREW_NO_INSTALL_CLEANUP.
Hide these hints with HOMEBREW_NO_ENV_HINTS (see man brew).