MacOS zsh alias pwd is incorrect
The $(pwd) in your alias command is replaced immediately by its value returned from execution. This occurs at the creation of the alias, not when you want to use the alias. As shown after your first run of alias myls, the alias contains the exact path, not a call to pwd, so this will always use the original path set when you created the alias.

To use the current directory, don't run pwd, just use a relative path, which will always refer to the current directory when run.

alias myls="ls -lrth ."