brew install --cask --appdir=/Applications docker
Updating Homebrew...
==> Auto-updated Homebrew!
Updated 2 taps (homebrew/services and mongodb/brew).
==> Updated Formulae
Updated 18 formulae.
==> Downloading https://desktop.docker.com/mac/stable/51017/Docker.dmg
######################################################################## 100.0%
Error: SHA256 mismatch
Expected: d63c7cc6d4fcbc1ef1fb113c7a594d90f4f44a2da2d1c7f3ed8d1553c5bc1bad
Actual: c03f7ebc91aaf2adf58fcf158a12a7b79b3be40aa59777397a7c00b98fc067eb
File: /Users/zhangli53/Library/Caches/Homebrew/downloads/a658405f2384261fc96fb40648ea5957f06c41a7081760738fa9d40a532609c0--Docker.dmg
To retry an incomplete download, remove the file above.
Mac 系统版本 10.15.7，在安装docker的时候，出现了下载了docker 的安装包后，因SHA256校验不通过的情况，网上说删除以下文件
cd /usr/local/Homebrew/Library/Taps/homebrew/
rm -f homebrew-cask
rm -f homebrew-core
再执行
brew update
To restore the stashed changes to /usr/local/Homebrew run:
'cd /usr/local/Homebrew && git stash pop'
To restore the stashed changes to /usr/local/Homebrew/Library/Taps/homebrew/homebrew-cask_bak run:
'cd /usr/local/Homebrew/Library/Taps/homebrew/homebrew-cask_bak && git stash pop'
To restore the stashed changes to /usr/local/Homebrew/Library/Taps/homebrew/homebrew-core_bak run:
'cd /usr/local/Homebrew/Library/Taps/homebrew/homebrew-core_bak && git stash pop'
==> Downloading https://mirrors.tuna.tsinghua.edu.cn/homebrew-bottles/bottles-portable-ruby/portable-ruby-2.6.10_1.el_capitan.bottle.tar.gz
##O=- # #
curl: (22) The requested URL returned error: 404
==> Downloading https://ghcr.io/v2/homebrew/portable-ruby/portable-ruby/blobs/sha256:61029cec31c68a1fae1fa90fa876adf43d0becff777da793f9b5c5577f00567a
#################################################################################################################################################################################################################### 100.0%
==> Pouring portable-ruby-2.6.10_1.el_capitan.bottle.tar.gz
==> Tapping homebrew/core
Cloning into '/usr/local/Homebrew/Library/Taps/homebrew/homebrew-core'...
remote: Enumerating objects: 1468747, done.
remote: Counting objects: 100% (480/480), done.
remote: Compressing objects: 100% (191/191), done.
remote: Total 1468747 (delta 295), reused 459 (delta 289), pack-reused 1468267
Receiving objects: 100% (1468747/1468747), 385.40 MiB | 5.49 MiB/s, done.
Resolving deltas: 100% (1030056/1030056), done.
Updating files: 100% (6978/6978), done.
Tapped 2 commands and 6630 formulae (6,989 files, 441.5MB).
Updated 2 taps (homebrew/cask_bak and homebrew/core_bak).
==> New Formulae
。。。。
You have 29 outdated formulae installed.
You can upgrade them with brew upgrade
or list them with brew outdated.
到最后更新是成功了，重新安装
brew install docker --cask
Running `brew update --auto-update`...
==> Caveats
If your CLI tools were symlinked to $HOME/.docker/bin your path should be modified to include:
$HOME/.docker/bin
==> Downloading https://desktop.docker.com/mac/main/amd64/93002/Docker.dmg
######################################################################## 100.0%
==> Installing Cask docker
==> Moving App 'Docker.app' to '/Applications/Docker.app'
==> Linking Binary 'docker-compose.bash-completion' to '/usr/local/etc/bash_completion.d/docker-compose'
==> Unlinking Binary '/usr/local/etc/bash_completion.d/docker-compose'
==> Backing App 'Docker.app' up to '/usr/local/Caskroom/docker/4.15.0,93002/Docker.app'
==> Removing App '/Applications/Docker.app'
==> Purging files for version 4.15.0,93002 of Cask docker
Error: It seems there is already a Binary at '/usr/local/share/zsh/site-functions/_docker'
又报错了，真的烦了。索性就直接页面上手动双击 f3d0b15869d33111de2f3f1850ccbd5ec589f6c377a52c3412001fff26ae26c6--Docker.dmg ，直接安装了起来，最后，还安装成功了。
所以 最后的解决方案是，并没有去关心docker Error: SHA256 mismatch，直接安装就完了。