Looking at members' Profiles, I no longer see the notice as to when the individual was last heard from. Has it been deleted?
Stack Overflow-the-company made some changes to user profiles in early August 2021, which, let's say, were not taken very positively: Some changes to the profile while we make it responsive
The "last seen" part of your profile is now only visible to you and the moderators on each site. So, unless you are a moderator, you cannot see anybody else's "last seen".
In a comment, animuson (SO staff) wrote that
We've actually had quite a few complaints in the past that a "Last seen" indicator public visible is a creepy and intrusive thing to have on a user profile.
The top response to that linked post is basically a complaint about this, and contains links to other answers arguing for and against the change, if that's of interest to you. (Personally, I don't really have a strong opinion on it either way, although if privacy is a concern, then it certainly makes sense to at least put it behind a flag.) But anyway, that's what happened to it.