While installing the Exchange 2019 Management Tools (only the Management Tools) on a server, I ran into the error message “A reboot from a previous installation is pending. Please restart the system and then rerun Setup”

Normally a reboot fixes this problem, but unfortunately this time it did not fix it.

The option to reboot is also logged in the registry of the server. There is a key called PendingFileRenameOperations located in HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Session Manager which in this case has a certain data that was not cleaned up previously:

When you check the data you can even see which process did not clean up. Remove the data from the key (or remove the entire key) and continue with the installation.