It is the 'Unity Patched Version' of VR Tablet PC for Valve Index device to solve the recent Unity security issue.
[Unity Patched Version] VR Tablet PC for Valve Index
Source: Steam Community (opens in a new tab)
Build and release context
Steam update times within 24 hours of this post. Matching dates do not confirm which build it describes.
Build 20413910 · public branch
Steam updated · First observed