The version 8 of PHP is scheduled for December 2020. All active extension must be upgrading their code to need a run with the new version.
Actually in development, the version 1.0 of the extension Win32Service will be compliant only with PHP 8. The version 1.0.0-dev is already upgraded and usable for tests. You can download the snapshot build of PHP for Windows (on the bottom of the page) and the Win32Service extension DLL on the GitHub repository.
Currently, version 1.0 of the Win32Service extension is building only for the x64 architecture and for two PHP mode (NTS and TS).