It appears to have been marked as “Deprecated” on the 6th of February, and was added on the 23rd of October, 2023:
(The dates show up if you hover over the version numbers.)
Because they were marked as Deprecated, it won’t show up in the properties window, however, it does still exist. Scripts should still be able to read and modify it, but it isn’t a good idea. Given that this property was only “supported” for 4 months, before mysteriously disappearing, they may have walked back on their decision to add it in the first place and might remove it completely.
However, the Release Notes for Version 600, the version this was added in, does actually explicitly mention it:
Given this fact, this might be a mistake. Maybe someone removed it by accident, not realizing they had announced it as a feature? I will post a Bug Report about this.
EDIT:
I have created the Bug Report here: