Earlier quoted context omitted.
No, the default Homebrew install location moved to /opt/homebrew on new Apple Silicon Macs. (I don’t know why Intel Macs still use /usr/local.) In any case, it’s possible to choose a custom installation location, even on Intel Macs if you prefer. https://docs.brew.sh/Installation Further discussion on the decision: https://github.com/Homebrew/brew/issues/9177
/opt/homebrew isn't a folder provided by the operating the system, but it's still a "system folder" as in not a user folder. That's messed up. I have to imagine that this causes no end of issues on multi-user machines. The homebrew folder should either be somewhere under ~, or owned by root or some other system account.
Nothing stopping you from having this owned by a system account, it's just not a path we recommend because it's not the best fit for most of our users.