Muv-Luv Regenerative Vol. 04 · published
On July 10th, some users reported issues launching the game after updating their Steam clients to the newest version.
Valve has applied a patch that should correct this issue.
(See: https://steamcommunity.com/groups/SteamClientBeta/discussions/0/3805027864671264896/?tscn=1689035343)
Thank you Valve for your quick response!