So the manual installer says that update is installed. But Windows Update requires restart. I've done it several times but nothing has changed. It still requires restart...
I faced the same problem however I have had this problem back in 23H2 version.
The fix is pretty simple, you go to the settings, updates, in the bottom tabs there is "Pause updates for 1 week" Once you press it, you have to click on Resume updates and it scans the current version by verifying that you already have the KB5050009 Update installed and the issue is fixed.
If your PC was running Windows 10 previously and you did update it without performing clean installation with removing everything (including partitions)
Most probably your recovery partition is too small to run updates above 500 Megabytes (Since back in the days the updates were not larger than 500 Megabytes and as of today, they can reach up to 600 Megabytes). If that's the case you should extend the recovery partition size up to 642 Megabytes.