Noted, thank you. Shortly after I post the question, I found the documentation link, I will test PHP 8 on dev server and report if I find any issue.
Q: Can I upgrade the PHP 7.4.x version to a higher version?
A: The FreePBX Distro comes by default with the supported PHP 7.4.x version. Updating the Distro PHP version is not recommended. Anyone who wishes to can try an updated PHP version for non-distro or custom installations, and report issues to the issue tracker as they find them.