The first-gen HoloLens is considered a prototype device, and it looks like it’s going to be left behind. Microsoft announced in support documentation that this version will be entering a Long Term Servicing state and will not get any operating system updates. “Future updates will focus on issue and security fixes, while maintaining feature parity with the Windows 10 October 2018 release for HoloLens (also known as RSS).” This means that the features introduced in Windows 10 May 2019 Update onwards will not be coming to the device. Those updates will only be available on the HoloLens 2.
Source: MSPowerUser