Some updates are prerequisites for others. One update might stay "pending" because it is waiting for a different one to finish installing and for the system to restart.
The files are on your disk, but the installation process has not yet begun. what does pending install mean on windows update
In short:
However, it becomes a problem when:
Most significant Windows updates cannot install while the operating system is running. They require a restart to swap out system files that are currently in use. If you see "Pending Install," it is almost always a signal that Some updates are prerequisites for others