https://wccftech.com/microsoft-hold-macs-updating-to-windows-10-1903-compatibility-issue/

The latest Windows 10 1903 has managed to steer clear of any major issues. However, Mac users have been having problems with the upgrade process. Microsoft has today said that it’s blocking some Macs from updating to Windows 10 May 2019 Update due to a compatibility issue. The issue only affects older machine or newer devices but with older versions of Apple Boot Camp or Windows Support Software drivers installed.

“Mac devices prior to 2012 or newer Mac devices with the older Apple Boot Camp or Windows Support Software drivers have a compatibility hold in place and are unable to update to Windows 10, version 1903,” Microsoft writes.