If the Windows Update page notifies May 2020 feature update is available and if you proceed with its download and Install, you may get a notification that asks you to “restart your PC to finish installing a firmware update”. This notification reportedly persistently appearing despite multiple restarts.
Windows 10 2004 has a lot of issues now. Recent July Cumulative Update has fixed some and removed Notepad and paint for some. This could be that feature update that most users aren’t being able to upgrade to.

Microsoft has blocked the update on its own Surface devices also.
Windows 10 May 2020 Update is available for 1903 and 1909 versions. Users running these versions, can manually check for updates and install the update if offered.
If the latest Windows 10 version is available to you, you’ll receive a notification like this on the Windows Update page.

When you proceed to update, you may receive unsupported Settings notification or installation won’t’ continue due to OneDrive. The Settings are not supported issue can be fixed by installing Windows 10 2004 offline.
One user reported on Microsoft forum that he is unable to install Windows 10 2004 as Windows is asking to restart the device to complete installing the firmware. But despite multiple restarts, the notification appears consistently. Here is what needs your attention notification says:
“The following things need your attention to continue the installation and keep your Windows Settings, personal files, and apps.
You need to restart your PC to finish installing a firmware update. Plugin your PC, make sure the battery is fully charged, restart, and then try installing again”.
Here, Windows 10 couldn’t able to install firmware updates via Windows Update, meanwhile, it is asking the user to fully recharge the laptop battery before restarting the device.
The affected user ends up updating the BIOS manually to get the notification away.
Related articles:
Microsoft releases Disk Cleanup Troubleshooter for Windows 10 2004
Windows 10 2004 Install with Media Creation tool is failing for Some
OneDrive is blocking Windows 10 2004 installation for some devices
Microsoft blocking Windows 10 2004 upgrade with “Your PC Settings aren’t supported” error