Windows 10 May 2019 Update (version:1903), which is now available, has a minimum storage requirement of 32 GB for both 32-bit and 64-bit to accommodate some space for updates, apps and temporary files for a smooth running system..
Now Microsoft has clarified some doubts on the new storage requirement and said that this rule is applicable for new devices only.
With the Windows 10 May 2019 Update (version: 1903), Microsoft has introduced a new behavior named "Reserved Storage", which will retain about 7 GB of free disk space for the updates to install smoothly.
For this to accommodate, Microsoft in a support document bumped up the minimum storage requirement of Windows 10 to 32 GB for both 32-bit and 64-bit systems.
This caused some confusions to new and existing users. Now, Microsoft has clarified this requirement and said that it will be applicable to only new devices. The manufacturers need to keep at least 32 GB free space in those new devices to install Windows 10 May 2019 Update (version: 1903). Here's what Microsoft said about it on the new support document:
New disk space requirement for Windows 10, version 1903 applies only to OEMs for the manufacture of new PCs. This new requirement does not apply to existing devices. PCs that don’t meet new device disk space requirements will continue to receive updates and the 1903 update will require about the same amount of free disk space as previous updates.