In zsh, including on macOS, you should add entries to your path in your .zshrc. By default this file is read from the directory located in $ZDOTDIR which defaults to $HOME if not set.
To add an entry there, you may follow instructions for bash and add a line such as:
export PATH=/opt/apache-maven-3.8.2/bin:$PATH
or because zsh also offers an interface to the path in the $path environment variable, which is an array, you may also use:
export path=(/opt/apache-maven-3.8.2/bin $path)
Either of these will add /opt/apache-maven-3.8.2/bin to your path before the previous contents of the path.
The order is important particularly for programs such as zsh which may be present at /bin/zsh and at /usr/local/bin/zsh, as would be the case if it is installed using homebrew (/bin/zsh being the default installation). If you install it separately, you probably want to use it and so should make sure that /usr/local/bin precedes /bin on your path, so to add it you should use:
path=(/usr/local/bin $path)
in that order. And don't forget to export it after updating it with export path
or precede path=
with export
.
If you are heavily customizing your zsh installation, you may be tempted to set the path in $ZDOTDIR/.zshenv. This should be avoided. Prior to loading that file, /etc/zprofile is read, which in a default macOS installation executes:
if [ -x /usr/libexec/path_helper ]; then
eval `/usr/libexec/path_helper -s`
fi
Which will screw the ordering of any customizations to your path. See the zsh man page with man zsh
for the details of the load order or man path_helper
for an explanation of that utility.