Homebrew does not support OpenJDK@8 on Apple Silicon (M1/M2) but Zulu Community 8 is present as a cask. You just have to enable cask-versions repository and install zulu8 cask.
brew tap homebrew/cask-versions
brew install --cask zulu8
It will install the JDK in /Library/Java/JavaVirtualMachines/zulu-8.jdk/Contents/Home. You should then configure your JAVA_HOME variable for development tools to use it.
export JAVA_HOME=`/usr/libexec/java_home -v 1.8`
Please note that Zulu Community 8 will only be supported until March 2026.