Issue appears to be fixed with 2.8.54 Thanks!
Please do not remove the download web page for versions prior to the current one, to allow to reinstall an older one as a workaround. I second this. At the very least, the most recent previous release should remain available to download. After the Windows key stopped working, I rolled back to 2.8.27 after downloading the installer from another site.
Keyboard layout on server and remote is U.S. English. Both systems are running 64 bit Tight VNC on Windows 10 Pro 64 bit release 20H2. I rolled back to 2.8.27 without making any other changes, and the Windows key once again started working.
2.8.53: Windows Key not detected